In April 2003 she joined Topzwemmen Amsterdam (TZA) to train as a full-time professional under the guidance of Fedor Hes. At the 2003 World Aquatics Championships it turned out to be a great decision as she reached two individual finals in the 50 m freestyle ending 7th, and in the 100 m freestyle finishing 8th. In Barcelona she also reached the final in all relay events but did not win a medal. In December she participated in the European Short Course Swimming Championships 2003 where she won her first international titles in the 50 m freestyle and the 4×50 m freestyle. In Dublin she also won silver in the 100 m freestyle and bronze in the 4×50 m medley. 2004 started off with the 2004 European Aquatics Championships in Madrid. There Veldhuis won two silver medals in the 4×100 m freestyle, together with Chantal Groot, Annabel Kosten and Inge Dekker, and individually in the 100 m freestyle. At the end of the week there was a bronze medal in the 4×100 m medley relay alongside Stefanie Luiken, Madelon Baans and Chantal Groot.