May was accepted as a Church Mission Society (CMS) missionary for the Roper River Mission on the 5th February 1923. She left for the north in March arriving at the Roper in May joining Louisa Cross in caring for the half-caste children there. In September 1924 she accompanied thirty-five children when they were transferred to Emerald River, Groote Eylandt and worked there for the next six years until the mission devoted its full attention to the Groote Eylandt Aborigines. May was on extended sick leave from July 1932 to December 1933 when she was asked to return to Groote immediately. She was reappointed as permanent missionary on 13 May 1935. In 1938 she attended lectures in anthropology at the Sydney University returning to north by flying boat in November 1938. May was transferred to Oenpelli and worked there until the evacuation of the mission and half-caste women and children in 1942. She cared for the seventy-seven children from the Territory at the Hostel in Mulgoa, New South Wales remaining with a group of children until they transferred back to Alice Springs in 1945. She retired in 1946 the CMS recognised her for devotion and long service.,