If Amy Tan's life was a novel, you'd think it far-fetched. She has been stalked and held at gunpoint but it seems luck is on her side, the bestselling writer tells Lisa Allardice

At a dinner at the British embassy in Washington, Amy Tan once met Margaret Thatcher. "She came up to me and I had my little dog and she was petting my dog and she said [Tan puts on a falsetto British accent], 'Oh, your book is so important, so courageous,' and I was thanking her and thanking her and she was going on and on, 'I was so moved when I read Wild Swans.' And I finally figured [ it out] and said, 'Yes, didn't Jung Chang do a wonderful job?' And she said, 'Yes, she did!' And we both did the very British thing and covered it up immediately."

Tan, who has always disliked the "writer of colour" tag, is surprisingly amiable about such incidents. "Jung Chang, Maxine Hong Kingston, Iris Chang, even Lisa See, who doesn't look Chinese at all - we all constantly get mixed up with each other," she says.

Dressed in floaty Issey Miyake trousers, a silk scarf and ornate jewellery, Tan looks positively glowing and nothing like her 53 years when we meet in a flat in Chelsea, London. Her answers are long and thoughtful, and tend toward the whimsical. But she is as charming and funny as you would expect the author of the much-loved novels The Joy Luck Club and The Kitchen God's Wife to be - if a little earnest at times.

Tan has been writing about her life growing up in a Chinese immigrant family in postwar America, in one way or another, since she first made her name with The Joy Luck Club in 1989. The combination of up-beat American pragmatism and Chinese exoticism, and her winning mix of sentimentality and spiritualism, have made her novels international bestsellers.

Apart from her mother's bouts of depression, the family were happy until Tan's father and brother both died of brain tumours within a year of each other when she was a teenager. The first dose of bad luck. Since then, there's been more - luck is a subject that repeatedly crops up in interviews with Tan. She tells me that over the course of her life she has been molested (by an acquaintance of her mother), held at gunpoint, beaten up, stalked, involved in two different car crashes on the same day, airlifted to safety during a mudslide, and that she once discovered a dead body.

If her life was a novel, you'd think it far-fetched. Some might say she is accident-prone, or even jinxed, but Tan thinks it must be luck: "I've been tested so many times and I've come through virtually unscathed," she says.

Tan has spent her life navigating through the conflicting belief systems she inherited from her parents: the Christian faith of her father, a Baptist preacher, whom she adored, and the Chinese superstitions and morbid imagination of her mother.

"She was all over the place. She had these hare-brained ideas about karma and reincarnation and why my brother and my father died so close together." Her mother dominates her fiction.

With their comforting fortune-cookie wisdoms on love, fate and respecting your elders, some critics have found Tan's novels a little bland. One snootily dismissed her as "no intellectual". Tan stopped reading reviews after another wrote that it was a big mistake to think her own life was so interesting that anyone should want to read about it.

Perhaps her huge popularity has counted against her with the literary establishment. When The Joy Luck Club was nominated for the National Book Award and the National Book Critics Circle Award (two big American literary prizes), her editor prayed that it would fall off the bestseller list because otherwise it wouldn't win. It didn't - and she didn't win.

But The Joy Luck Club (which has also been turned into a successful film) has certainly made Tan something of a literary celebrity. She is part of an unlikely lit-rock band called The Rock Bottom Remainders, along with Stephen King and Barbara Kingsolver, which raises money for inner-city children. (It is hard to imagine this neatly dressed woman in full dominatrix outfit, including leather boots and wig, but her repertoire only extends to These Boots Were Made for Walking and Leader of the Pack.)

Matt Groening, creator of The Simpsons, is also a member of the band, and Tan has starred in an episode of the show where Lisa Simpson goes to a book fair to meet all her favourite authors. After Tan has finished reading, Lisa puts up her hand and says: "Miss Tan, I just love the way you demystify mother-daughter relationships in your fiction." Tan replies: "That's not what my books are about. Sit down. I'm ashamed for the both of us."

What Tan found most amusing was that John Updike was also at the festival, but presumably because he could not be persuaded to take part, his character was speechless. "He would barely start to say something and someone would say, 'Shut up, Updike, shut up, Updike.' "

She laughs as if she has heard the joke for the first time. This was the only occasion when Tan didn't object to being portrayed as "yellow-skinned".

Perhaps even more than the stories of her Chinese ancestry, Tan is indeed best known for her witty "demystification of mother-daughter relationships". So why did she and her husband of more than 30 years, Louis DeMattei, choose not to have children?

"At first it wasn't a firm decision. I thought, well, I will think about that later. Did I feel I need to replicate myself genetically? No - because there's probably a lot of bad stuff in that genetic pool. Did I feel my marriage would be incomplete without children? No. Was I selfish? Probably, yes. I know now that if I had children I would experience a kind of love I couldn't have with anyone else. But looking back, do I feel I have a deep loss and regret? No, I don't. Because I was also able to have this other kind of love that I experience through writing."

You don't have to be an expert to write about motherhood, Tan says, "maybe just a confused obsessive about fractured family relationships. Maybe I couldn't have written as honestly if I'd had a daughter of my own."

It is this honesty that gives her novels their universal female appeal. The Joy Luck Club once came top in a list entitled "Books Women Love - And Men Don't Get". As Tan says: "There happen to be a lot of mothers, there happen to be a lot of daughters. Half the world includes people like that - at some point they all think, I didn't have a perfect relationship with my mother and maybe one day my mother might go away and it would be a terrible thing not to know this person a little better."

Tan's mother died in 1999, having suffered from Alzheimer's. Then, in another cruel run of luck - or fate - her long-term editor and close friend, Faith Sale, died from cancer 10 days later. Tan had lost the two most important women in her life, but she has a remarkable ability to see the world revolving around her own emotional axis, not in a self-centred way, but simply as a matter of fact.

"It was the best time it could have happened to me, because when my mother died Faith was going in for surgery, and I was already in this strange place that you are when you think about life and death, memory and everything."

At the time, Tan was finishing her fourth novel, The Bonesetter's Daughter, and had moved to New York to be closer to Sale. Following her mother's death she felt she had to rewrite the ending completely. Then, less than an hour later, she began her latest novel, Saving Fish From Drowning. It has only just been published because for a while, she became physically incapable of writing.

"In 2000 I became really, really afraid. I felt there was darkness all around me. I had this sensation that there was always a knife aimed at my back. I couldn't leave the house by myself. I would check the doors. It was the constant presence of danger and the expectation that something terrible was about to happen."

She was diagnosed with depression and post-traumatic stress. Then the doctors thought it must be something more serious."They said it could be a tumour in your pancreas, it could be a brain tumour - none of them sounded good. Then 9/11 happened and I thought, 'Who cares if I've got cancer - we're all going to die'. I didn't feel any more fearful. I guess I felt: now everybody feels how I've been feeling for a while. That something awful is going to happen."

Eventually, she was diagnosed with Lyme disease, the result of a tick bite at an outdoor wedding more than four years earlier. As soon as she began to be treated, her head cleared and the world seemed a lucky place once more. She will probably always be on medication, but the side effects are good ones. The pills make her "a little too happy", but she was able to finish her novel.

Saving Fish From Drowning is a witty parable, loosely based on The Canterbury Tales, about 12 American tourists who mysteriously disappear while on a trip to Burma. It is tempting to read this morality tale about a group of well-meaning Americans and their hapless "group leader", blundering into a foreign country, as a satire on the Bush administration's gung-ho foreign policy. Tan seems pleased by the idea, but it wasn't deliberate. She started the novel well before 9/11, but as she got to the end she was struck by how much it reflected world events.

The story is narrated by an eccentric, opinionated art dealer - who has died in bizarre circumstances a few weeks before the trip. At first this seems not only implausible, but an altogether different novel from her previous fiction: most of the action takes place in Burma, only two of the characters are Chinese (one of whom is the dead narrator), and, most striking of all, the mother and daughter relationships are entirely incidental to the plot. Is this because of her mother's death?

"When my mother died, I did think that maybe I wouldn't be writing about her any more. But then I heard her say, 'Well, I can still tell the story! I don't have to be your mother in it.' And I thought, 'OK, you can tell the story, you can be the narrator.' So I made the narrator dead just like my mother was dead. I took her voice, and by voice I don't mean her broken English, but the way she looked at the world." Like all her other fiction, then, this is still all about her mother.

Tan chose Burma because she was offered a place on an art expedition there, and was faced with the moral dilemma as to whether she ought to go. When she learned that writers were not allowed into Burma, her mind was made up. "I put on my visa that I was a consultant to a children's programme because I was working on a TV series based on a children's book of mine."

The title, Saving Fish From Drowning, came from a Burmese guide book. It is an expression to describe the logic used by Buddhist fishermen to avoid bad karma - by removing fish from water, they are saving them from drowning. It was a wonderful metaphor for the questions of moral ambiguity and responsibility she wanted at the heart of the novel. Part of the story is based on the accounts of the suffering of the Burmese people she found on chatrooms and human rights sites on the internet, in particular the mass rape, mutilation and murder of the Karen tribe.

"When I had to write that section I literally felt sick to my stomach. So if I had started off that way, I don't think I could have written it. And if I couldn't have written it, who would have wanted to read it?"

But is a farcical parable about a bumbling bunch of tourists really a suitable vehicle for such grim material? "I approached [ the South African writer] Nadine Gordimer with that very question. I asked, 'Can you take a very dark serious subject about human rights abuses and write it as a comedy?' She said, 'Absolutely - sometimes it's the only way.' I thought about doing it in a darker way, but I decided it would border on being moralistic, rather than using the seduction of fiction to do what it can best, which is to be subversive."

While Saving Fish From Drowning is as engaging and sparky as ever, Tan fans may be disappointed not to find the heart-tugging narratives they have come to expect. Just after the publication of The Joy Luck Club, Tan was dismayed when an enthusiastic reader rushed up to her and said: "How does it feel to have written your best novel first?"

Five novels and 15 years later, does Tan feel she was right? "I accept that probably for the rest of my life I will be identified with The Joy Luck Club. On my tombstone - if I wanted a tombstone, which I don't - it would say: 'Author of The Joy Luck Club'. That's fine. I hope that I continue to write my best book with each book that I write. I am very lucky that that happened to me." - Guardian service

• Saving Fish From Drowning is published by Fourth Estate