Melachroinou competed for the Greek squad in a butterfly double at the 2000 Summer Olympics in Sydney. She achieved FINA B-standards of 1:01.50 (100 m butterfly) and 2:15.24 (200 m butterfly) from the European Championships in Helsinki, Finland. On the first day of the Games, Melachroinou placed thirty-fourth in the 100 m butterfly. Swimming in heat three, she edged out South Korea's Lee Bo-eun on the final stretch to grab a second seed by 16-hundredths of a second in 1:02.06. Three days later, in the 200 m butterfly, Melachroinou posted a seventh-seeded time of 2:17.60 to hold off a sprint challenge from Singapore's Christel Bouvron by a small fraction of a second in heat two, but finished farther from the semifinal field with a thirty-first-place effort.