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.
After she missed out all international tournaments in 2004 and 2005 she returned to international competition in Budapest to compete in the 2006 European Aquatics Championships. Meanwhile she started to train with the Nationaal Zweminstituut Amsterdam where she is coached by Martin Truijens. She only started in the 4×200 m free ending up with an 11th place. Although she didn't meet the qualifying standards she was selected for the 2007 World Aquatics Championships in Melbourne, Australia and started in the 4×200 m freestyle relay which reached the final and ended third.
At the 2008 Summer Olympics she started in the heats of the 4×100 freestyle relay alongside Ranomi Kromowidjojo, Femke Heemskerk and Hinkelien Schreuder. But she and Schreuder were replaced for the final by Inge Dekker and Marleen Veldhuis. Van Rooijen saw her team-mates win the final and received a Gold Medal for her efforts in the heats. Together with Heemskerk, Kromowidjojo and Saskia de Jonge she swam the heats of the 4×200 m freestyle but they failed to qualify for the final.