Van Rooijen made her international senior debut at the European LC Championships 1999 in Istanbul, Turkey with 4th places in both 4 × 100 m freestyle and 4 × 100 m medley relay. One year later she started again in the European LC Championships this time it took place in Helsinki, Finland. There she started individually in the 100 m and 200 m freestyle ending up 17th and 24th. In the 4 × 200 m freestyle relay there was a 7th place. In September 2000 she competed at the Sydney Olympics where she won a silver medal in 4 × 100 m freestyle relay together with Inge de Bruijn, Wilma van Hofwegen and Thamar Henneken. There was also an 11th place in the 4 × 200 m freestyle.