Van Rooijen left for the United States in January 2001 to study at the University of Miami. She kept her place in the national team during the 2001 World Aquatics Championships in Fukuoka, Japan which turned out te be a disappointment. In both relays, 4 × 100 m and 4 × 200 m freestyle, she and her team were eliminated in the heats. She reached her first individual final in 2002 in Berlin at the 2002 European Aquatics Championships finishing 8th in the 200 m freestyle. There was also a bronze medal for her in the 4 × 100 m freestyle relay together with Marleen Veldhuis, Chantal Groot and Wilma van Hofwegen and a 5th place in the 4 × 200 m freestyle. At the 2003 World Aquatics Championships in Barcelona she just missed out for a world championship medal by finishing 4th in the 4 × 100 m freestyle. She also achieved a 7th place in the 4×200 freestyle. After three years she returned home and found a place in Dordrecht, with Topzwemmen West-Nederland under the guidance of trainer-coach Dick Bergsma but failed to qualify for the 2004 Summer Olympics due to a severe shoulder injury.