Gibney competed in four individual events, as a member of an Irish squad, at the 2000 Summer Olympics in Sydney. After finishing tenth from the European Championships in Helsinki, Finland, her entry time of 2:02.83 (200 m freestyle) was officially accredited under a FINA A-standard. On the second day of the Games, Gibney placed thirty-fourth in the 400 m freestyle. Swimming in heat one, she enjoyed the race with an early lead in the first 150 metres, but faded down the stretch to a fourth seed in 4:23.73. The following day, in the 200 m freestyle, Gibney produced her best result with a twenty-eighth-place effort in 2:05.24. Two days later, in the 100-metre freestyle, Gibney placed forty-second on the morning prelims. Swimming in heat three, she fell short on the final lap to a seventh spot in 58.79, a 2.1-second deficit from leader Olga Mukomol of Ukraine. In her fourth event, 50-metre freestyle, Gibney posted a time of 27.46 from heat five, sufficiently enough for forty-eighth seed in the prelims.