Houston Judge David Hittner turned aside pleas to give Lea Fastow only a few months in prison for filing a false tax form. The plea came after months of legal wrangling.
Judge Hittner gave her no fine but placed her on a year of supervised release once the sentence is completed.
"I've made errors in judgment I will always regret for the rest of my life," she told the judge. "But I can't undo the past. I am only able to do what is right now."
US energy conglomerate Enron imploded into bankruptcy in late 2001 amid a series of questionable financial transactions.
The collapse cost thousands their jobs and erased the investments of thousands more who owned its stock.
Lea Fastow, 42, was a former assistant treasurer there, but the case against her solely involved her role in her and her husband's tax filings.
Both prosecutors and defence lawyers had urged Judge Hittner to show leniency and limit Lea Fastow's prison confinement to five months, with another five months of home confinement, to minimise her time away from the Fastows' two young children.
Her case was part of a global deal that included a plea agreement for Andrew Fastow. He pleaded guilty in January to two counts of conspiracy, admitting to running widespread schemes and partnerships to make Enron appear financially healthy while enriching himself at the company's expense on the side.
He agreed to relinquish more than #13 million in cash and property, serve the maximum 10 year prison sentence on two counts of conspiracy and help prosecutors pursue other cases.
His help led to subsequent indictments of former Enron chief executive Jeffrey Skilling and former Enron top accountant Richard Causey.
Judge Hittner rejected the plea agreement, saying he refused to be bound by the sentence her lawyers had worked out with prosecutors. He said he wanted to consider the 10 to 16 months called for by federal sentencing guidelines.
Lea Fastow was born to one of Houston's most respected old-line families, the heiress to a grocery and property fortune.