Porter was independently wealthy and bred and raised Sheltie dogs at a kennel she owned in Georgetown, Connecticut.
She began an internship at the Massachusetts State Industrial School for Girls under Mary Williams "Molly" Dewson, superintendent of parole, who became her lifelong partner.
[1][4] In 1922, they moved to 171 West 12th Street; in the same building lived Marion Dickerman and Nancy Cook, Grace Hutchins and Anna Rochester.
[5][6] Nearby, at 20 East 11th Street, lived Esther Lape and Elizabeth Fisher Read.
During summer 2017, the Castine Historical Society held the exhibition "Castine’s Devoted Women: Partnership and Social Reform 1910-1962" focused on Mary W. "Molly" Dewson and Mary G. "Polly" Porter.