Career
Kosten made her international debut at the European LC Championships 2000 in Helsinki, Finland where she ended fifth in the 4×100 meter freestyle relay, she did so alongside Thamar Henneken, Chantal Groot and Wilma van Hofwegen. She ended fourth in 4×50 meter freestyle at the European Short Course Swimming Championships 2002 in Riesa, Germany alongside Marleen Veldhuis, Suze Valen and Chantal Groot. 2003-2005
At the 2003 World Aquatics Championships in Barcelona, Spain Kosten teamed up with Manon van Rooijen, Marleen Veldhuis and Chantal Groot for the 4×100 meter freestyle relay, in which they reached the fourth position.
At the European LC Championships 2004 in Madrid, Spain she took home the silver of the 4×100 meter freestyle relay, her teammates were Chantal Groot, Inge Dekker and Marleen Veldhuis.
At the 2004 Summer Olympics in Athens, Greece Kosten swam in the heats of the 4×100 meter freestyle relay alongside Inge Dekker, Marleen Veldhuis and Chantal Groot. After the national championships in April 2005 Kosten retired from competitive swimming.