Mary considered leaving Saint Louis to attend college, but her parents insisted she stay for at least the first two years. In 1926, Mary entered Washington University, ultimately staying all four years to complete her degree. Mary majored in both English literature and political science and considered becoming a lawyer.
English Professor William G. B. Carson became one of her favorite teachers. Carson cast Mary in one of the yearly student plays he produced, and after her performance, he encouraged her to audition at the Saint Louis Little Theater. In addition to theater, Mary participated in honor societies, the debate team, Phi Mu sorority and the "Student Life" newspaper during her time in college.
Mary received her Bachelor of Arts degree in June 1930. After graduation, she worked at the university as the Assistant Publicity Director. She prepared press releases and articles, acted as liaison to students working on "Student Life", and worked on the early alumni magazine. During this time, she performed in a few University theater productions, continued to act with local theater companies and performed on various radio shows.