After an early teaching career, she completed her doctoral thesis on the development of preschool-aged Māori children, and began working for the New Zealand Council for Educational Research.
Her mother, Alma (née Fuller), was a clerical worker and her father, Gerald Player, was a public servant.
[1][2] She attended Hataitai School, where she was dux in her final year, and subsequently Wellington East Girls' College.
[3] Her father committed suicide when she was 13, which meant McDonald and her mother had to live with her terminally ill aunt.
[2] After graduating she taught the subject of clothing at Hutt Valley Memorial Technical College and studied part-time at Victoria University of Wellington, starting in 1944.
[2] In 1948 she completed her Bachelor of Arts and married; she then moved to London with her husband for three years, where she taught in secondary schools.
[1][2] In 1969 McDonald obtained her Master's degree with distinction, based on her study of playcentres in Wainuiomata, and developed an interest in Māori culture and the involvement of women in their children's education.
[2] While working on her studies she published the books Māori Mothers and Preschool Education (1973) and An Early Wellington Kindergarten (1975), both of which are still used by teachers and researchers today.
[2] In the 1990s she was the chairperson of the Future Directions Early Childhood Education Project, and the recommendations of this group were adopted by the Labour Party when it later came to power.
[3][5] In 1992 she retired from NZCER, but continued to work as a consultant and undertook some part-time lecturing at Wellington Teachers' College and Victoria University.