Mary Bethia Marshall was born on the 1st June 1886 at Gutcher in the north of the island of Yell in the Shetlands, Scotland.
She was the daughter of James Marshall and Catherine (nee Hoseason) who were married at 4 Fox Lane, Lerwick, Shetlands on the 1st June 1885.
Her mother was also from Gutcher whilst her father was from Dundas, near Edinburgh, Midlothian
Mary had at least three siblings who were all born after the family moved to Glasgow; John James and William R were born c.1888 and Agnes was born in 1891. The family were living at 68 Gourlay Street in the parish of St.Rollox, Glasgow, at the time of the 1891 census and James Marshall was working as a blacksmith .
Her mother, Catherine, died at Glasgow in 1893.
Mary Marshall's whereabouts between that date and 1911 has not yet been traced but in that year she was living at the nurse's home associated with Toxteth Park Workhouse Infirmary.
Her father's address was 22 Durand Gardens, Stockwell, London after the war. It is also thought that her brother John emigrated to Australia.
Mary Marshall was serving as a staff nurse Q.A.I.M.N.S. Reserve at the 37th General Hospital at Vertekop (now Skydra) near Monastir, Salonika, when she was killed in an air raid. The hospital had 1600 bed and was established in June 1916,
Two reports on her death appeared in the 'British Journal of Nursing'.
   The British hospital camps attached to the Serbian Army at Vertekop, which on three occasions last summer were bombed by German aeroplanes, were again attacked in similar fashion last week, with the result that several of the patients were killed or wounded and two British nurses lost their lives. These were Staff Nurse M.S. Dewar, Q.A.I.M.N.S. Reserve, and Staff Nurse M. Marshall, of the same Service. Staff Nurse D.E. Dodds, T.F.N.S., who was trained at the Willesden Infirmary, was wounded, but we are glad to know she is recovering/ There is absolutely no excuse for this new act of barbarity, because the hospital camps in question are situated a long distance from any other camps and are conspicuously marked with enormous red crosses painted on the ground.
   It is evident that the enemy bombarded them intentionally.

British Journal of Nursing 24th March 1917

Nurse Marshall's portrait appeared in the second report:
   A simple marble cross marks the grave of Miss Mary Marshall, an English nurse buried at Salonika, and as we have notified, killed while on duty in the operating theatre during an enemy air raid. The cross bears the inscription, "Sacred to the memory of Staff Nurse Mary Marshall, Q.A.I.M.N.S. (R.), 37th General Hospital, who was killed at the post of duty during an aerial bombardment on March 12th, 1917. 'In Arduis Fidelis." Erected by her comrades at the General Hospital."

British Journal of Nursing 11th August 1917

Mary Marshall and the other victims of the air raid were initially buried at Vertekop but after the war their remains were removed to Mikra British Cemetery.
Mary Marshall's posthumous award of the Croix de Guerre with Palms by France was reported in the press in 1917 but official notification only appeared in the London Gazette on the 18th August 1920.
The following appeared in the Benigonian on the 4th October 1917.
   According to an order of the day, published in the Paris "Official Journal" on the 23rd July, the Croix Guerre (with palm) has been awarded to Miss Margaret Dewar, a staff nurse at an English hospital, who was mortally wounded during the bombardment of the hospital while protecting a patient's head with a pillow.
   The decoration has also been awarded to Miss Mary Marshall, who was killed in the same aerial bombardment, and to an American volunteer names Lovering, who was in charge of an adjoining American establishment.
   Their courage in protecting the wounded earned for them the admiration and affection of their French comrades.
Ethel Garrett, Rebecca Colhoun, two of the nurses who survived the fatal air raid at the 37th General Hospital, were awarded the Military Medal:
Sister Dewar was struck in the chest by a piece of bomb casing that had exploded nearby as she knelt over a wounded soldier. Sister Colhoun went to her aid but she died in her arms. She herself did not escape injury during this air raid and was hit by a bomb splinter as she attended patients. Sister Garrett attended a soldier who had been wounded by a German bomb and had sustained a compound fracture of his skull. She risked her own life to administer life saving first aid. Whilst she was doing this 14 bombs fell within an 80 yard radius of their location.
Annie Rebecca Colhoun's M M citation in the London Gazette reads:
For conspicuous bravery and devotion to duty during an enemy air raid. She attended to, and provided for the safety of, helpless patients. She was assisting Staff Nurse Dewar when the latter was fatally wounded, and although the tent was full of smoke and acrid fumes, and she had been struck by a fragment of bomb, she attended to Staff Nurse Dewar and also to the case of a helpless patient