In 1938 she received her doctorate cum laude with a thesis titled Gods and Cults in Ptolemaic Alexandria.
[3] In 1946 Visser was named an assistant to David Cohen, at the University of Amsterdam, before he was deported to the Theresienstadt concentration camp by Nazi occupiers.
Cohen survived the war there and Vissar referred to him as her spiritual father in the preface of her doctoral dissertation.
Her style was described as characterized by a traditional, social-liberal sense of responsibility coupled with modern or conflict-avoiding leadership qualities, leading to her nickname Mater et Regina (queen and mother).
[1][3] In some publications, Visser also devoted herself to women and gender relations, such as in her lecture The Woman and Destiny in Greek Literature, in which she concluded that "whoever begins to sketch the picture of a woman in a certain period of literature ends up sketching the picture of the man in that period."