Mary was the youngest of the nine children of Isaac and Ann Gardiner.
After her father became superintendent of Rondeau Provincial Park in 1894, she did some of the stenographic chores in the park office. She also also aided her brother and assistant superintendent Herb Gardiner with his correspondence.
After Isaac's death in early 1913, she lived with Herb in the new assistant superintendent's house in the park. They became close friends with Algonquin Provincial Park superintendent George Bartlett and his family. Mary married George in 1922 after the death of his first wife and they moved to Ridgetown.