Gerritsen's breakthrough came during the 2004–05 speed skating season when she won the bronze medal in the 500 m at the 2005 KNSB Dutch Single Distance Championships.

She finished 12th in the 500 m and 23rd in the 1000 m. In the 2006–07 pre-season Gerritsen showed her potential to become the fastest Dutch sprint speed skater when beating teammate Marianne Timmer several times.

However at the 2007 KNSB Dutch Single Distance Championships she was unable to keep her pre-season form and only finished in third position behind the surprising Margot Boer and Timmer.

Her performances gave her the opportunity to participate in the 2007 World Sprint Championships, where she finished 7th overall, with a 4th place in the second 1000 m race.

Gerritsen won silver in the 1000 m at the 2010 Winter Olympics in Vancouver with a time of 1.16.58, only a fiftieth of a second behind gold medallist Christine Nesbitt of Canada.