At the 2000 Summer Olympics in Sydney, Muller competed in four swimming events. She achieved FINA A-standards of 25.94 (50 m freestyle), 55.82 (100 m freestyle), and 2:00.35 (200 m freestyle) from the South African Nationals in Johannesburg. In her first event, 200 m freestyle, Muller finished her semi-final run with a ninth-seeded time of 2:00.04. Earlier in the prelims, she posted a second-fastest time and a South African record of 1:59.89. Three days later, in the 100 m freestyle, Muller finished sixth in the final with a sterling African record of 55.19. In the 50 m freestyle, Muller posted a time of 26.07 from heat nine, but missed the semi-finals by 11-hundredths of a second. On the last day of the program, Muller teamed up again with Loots, Sarah Poewe, and Charlene Wittstock in the 4×100 m medley relay. Swimming a freestyle leg, Muller anchored the race with a split of 54.77, a new national record, but the South Africans settled only for fifth place in a final time of 4:05.15.