She then joined the First Aid Nursing Yeomanry service (FANY) as an ambulance driver, and for her gallantry in the field was awarded the Croix de Guerre by the French, and a Military Medal by the British. The London Gazette, in which the latter award was announced on 19 October 1918, noted that ‘Miss Stubbs was detailed to evacuate a hospital. While her car was waiting to be loaded a bomb dropped within 30 yards. The stretcher-bearers, who had been loading a car immediately in front, ran for protection to dug-outs, calling to Miss Stubbs to do the same. She, however, regardless of her own safety, stayed in the open with two wounded and helpless patients to help and reassure them. She finally got them unloaded and to a place of safety. During the unloading a second bomb fell on the hospital.’
Mary married John Keith Harvie in 1919 and had three children, Jackie, Donald and Kathy, whom she nicknamed Axie, Dood, and Bertie, respectively. She died from cancer on 4 August 1937 at the age of 43.