Born in Kingston, Rhode Island, USA, Fierro has been Ecuador's strongest female chess player for many years, and has represented Ecuador in ten biennial Chess Olympiads from 1994 to 2012. In 1998 she played in the open section (with both male and female players), while in the other editions she took part in the women's tournament. Her best results were when she scored 9.5/13 in the 1996 Women's Chess Olympiad in Yerevan, and 7.5/8 in the 2008 Women's Chess Olympiad in Dresden, to win the silver medal on board 1 on both occasions.