In 1998 Olaru moved up to senior competition, taking first place with the Romanian team and second on vault at the European Championships. The following year, she contributed to the team gold medal at the 1999 World Championships in Tianjin, China and became the second Romanian gymnast in history, after Aurelia Dobre, to win the all-around title. In 2000, she was, with Simona Amânar, Loredana Boboc, Andreea Isărescu, Claudia Presăcan and Andreea Răducan, a member of the Romanian team at the 2000 Olympics. There she shared in the team gold medal and won a silver in the all-around (after the Răducan controversy). She also qualified for the balance beam event final and placed sixth.