At the 2000 Summer Olympics in Sydney, Hem competed only in the 50 m freestyle. Invited to the Games as a wild card selection by FINA officials, she entered the race in her lifetime best of 34.78. She challenged six other swimmers in heat two, including Maldives' 13-year-old Fariha Fathimath. She scorched the field to a seventh seed in a Cambodian record of 33.11, edging Iraq's Noor Haki out to last place by 2.4 seconds. Hem failed to advance into the semifinals, as she placed seventieth overall in the prelims.