Mileisyte qualified for the women's 50 m freestyle at the 2008 Summer Olympics in Beijing, by clearing a FINA B-standard entry time of 26.32 in a time trial from the Seven Hill Trophy in Rome, Italy. She won the sixth heat by 0.28 of a second ahead of Papua New Guinea's Anna-Liza Mopio-Jane in a lifetime best of 26.19 seconds. Mileisyte failed to advance into the semifinals, as she matched her thirty-ninth-place tie with two-time Olympian and South Carolina Gamecocks swimmer Sharntelle McLean of Trinidad and Tobago in the preliminary heats.