She discontinued her work when the police began to show interest in kiosks selling nude photographs.
Helgoland, a popular bathing establishment on the outskirts of Copenhagen, attracted a number of photographers including Peter Elfelt, Holger Damgaard, Julius Aagaard and Sophus Juncker-Jensen.
[2] Well ahead of the huge interest in female nude photography which was to take off in the 1920s, Mary Willumsen's photographs from 1916 to 1920, though carefully posed, appear far more spontaneous than earlier work.
Portraying groups of smiling schoolgirls to grown women in different states of undress, her pictures are unique in their intimacy, their spontaneity and in the personal appreciation she had for her subjects.
[1] Much of the information we have about Mary Willumsen comes from a police report which was drafted after she was arrested in 1920 for producing and selling illegal postcards.
As time went by, a certain Mr Brix, the owner of the nearby Scala Book Kiosk, asked Willumsen to take some bathing pictures for him to sell.
As her business expanded, she extended her sales to kiosks in Istegade and the Circus Garden in the centre of Copenhagen.
Even if Willumsen's postcards were sold at the Scala kiosk to those looking for pornography, the Helgoland bathing establishment seems to have offered a level of openness where women could act naturally without behaving erotically.