The principal of Loreto High School Beaufort in Rathfarnham, where Lynsey O'Brien was a pupil, said students and staff were shocked by the news.
"It's a terrible thing. It beggars belief," said Liz Cogan. "Lynsey was a wonderful pupil, vibrant, healthy and very popular. She was very well liked by her teachers and was looking forward to her trip so much. We are only just beginning to digest the news here."
The transition-year student was involved in dancing, basketball and drama at the school and participated in all events with enthusiasm, Ms Cogan said.
One of her sisters is in fifth year in the school, and another is due to start at the school soon. "We all know her family very well - it's terrible," said the principal. "It's a very difficult time for all of us."
John Phelan, chairman of the Loreto Beaufort Parents' Association, said there was shock and devastation among parents and Lynsey's friends.
"Fourth years, transition years - they're very young women and they're totally devastated," he said.
"She was a lovely girl, popular, vibrant, a typical 15-year-old."
He said the principal and counsellors had been comforting Lynsey's classmates at the school yesterday and that prayers had been said for her.
