 Mary was a friend of Newnham's principal Eleanor Sidgwick.In 1890 Marshall became a member of the Ladies Dining Society several of whom were associated with Newnham College.The society was started by Louise Creighton and Kathleen Lyttelton; other members of the society included Eleanor Sidgwick, the classicist Margaret Verrall, Newnham lecturers Mary Ward and Ellen Wordsworth Darwin, the mental health campaigner Ida Darwin, Baroness Eliza von Hügel, and the US socialites Caroline Jebb and Maud Darwin.