Willemijn was born in Son en Breugel in the Netherlands, but grew up in Nuenen near Eindhoven. She graduated from the Rotterdam Conservatory, where she was coached by Laura de Bekker. Willemijn started playing with bands, but decided to do musicals. She started in the company of the Original Dutch Productions of Elisabeth and De Drie Musketiers. After her Dutch beginning she starred in the German productions of Elisabeth, We Will Rock You and Wicked.