Dorenfeldt found her first job in 1920 as an assistant at the chemistry laboratory at Royal Frederick University (now University of Oslo). A few months later, she was promoted to a secretary-like position, from which she could perform research and teach. Soon she was investigating the atomic weight of chlorine while working with the radiochemist and associate professor Ellen Gleditsch, who had previously worked with Marie Curie in Paris. Dorenfeldt helped publish their results in English, German and French.
In 1922, the university granted Dorenfeldt a scholarship so she could study at the Collège de France in Paris. While there she met and married a fellow Norwegian and changed her name to Margot Dorenfeldt Holtan. She published research using her married name as well as her maiden name.
As a wife and mother of two, Margot attended to her family but continued working in the field as a part-time secretary and chemist and, according to her own records, she also published scientific work with her husband. Throughout her life, she remained close to her father and his business interests and she took a government position in 1946 and then became an association board member from which she could help protect the interests of his pulp and paper businesses.