She started her international beach volleyball career already in 2002 at the age of 17. She teamed up with Arjanne Stevens with whom she became World Champion under 18. At the European under 18 Championships they reached the final as well, but this one was lost, resulting in a silver medal. That year they also won the under 18 tournament in Xylokastro. The talented team didn't last long and in the following year Keizer had a new partner called Merel Mooren. In no-time they were among the best teams in the Netherlands. They even became Dutch champions by breaking the run set by Rebekka Kadijk who was teaming up with Marrit Leenstra at that time. In 2004 they finished second behind this team, but they won the FIVB Satellite tournament in Lausanne. After the 2004 Summer Olympics Kadijk/Leenstra decided to split up. Mooren was Kadijk's next partner, while Keizer continued with Marrit Leenstra, with whom she did not reach any notable results with, except a 4th place at a tournament in Montreal.