De Marez Oyens was born as Woltera Gerharda Wansink. She studied at the conservatory in Amsterdam, with a major in piano. Here, her talent for composition was discovered as she wrote her first pieces. These included chamber music and song cycles. After that she came in contact with youth groups, for whom she also wrote individual pieces.
She then became the cantor of the Reformed church community of Hilversum. Because of this she was very busy with church music. She wrote 14 melodies for the church songbooks that appeared in 1973. The lyrics for these songs were supplied by, among others, Muus Jacobse, Willem Barnard and Ad den Besten, whom she knew personally.
In the sixties she experimented with the tone poem and electronic music. Sound and Silence (1971) and Mixed Feelings (1973) are pieces of electronic music she composed, and Pente Sjawoe is an example of a work in which the tone poem plays an important role.
In 1977 she became an instructor at the conservatory in Zwolle. Her lessons focused especially on the development of the student's own style. But she wanted to continue to write her own pieces and after the death of her second husband she became a full-time composer. At that time she wrote The Odyssey of Mr. Goodevil (1981). In 1988 she contributed pieces to the international cello competition in Scheveningen, and in 1989 she was composer in residence at the Georgia State University in Atlanta.
She wrote over 200 works of music, many commissioned by the Dutch Ministry of Culture and various broadcasting networks. In 1995 she was asked to write a piece (Unison) for the 50th anniversary of the United Nations.