Before pursuing a career in medicine, Mary Elizabeth Donaldson, M.D. was a grade school teacher in both Wisconsin and Idaho. It was her experience caring for her ill brother that strengthened her desire to enroll in medical school. She was the only woman MD graduate from Wooster University in Cleaveland, in 1892. Once she returned to Boise with degree in hand, Mary and her husband (Thomas L. Johnston) founded the Idaho Sanitarium Institute, a spa-like institution meant to prevent and cure disease through proper diet and exercise in which she gave free medical care. She expanded her practice from 1894 to 1898 by setting up similar institutions in Milton, Oregon and Portland, Oregon. Her practice in Boise became so successful that Mary was able to give free or reduced-rate services to those in need.

Dr. Donaldson said: "It is not from the few spectacular or so-called great deeds that the blessings of life chiefly come, but from the little ministries that fill the every days."

She and her third husband (Captain Gilbert Donaldson, a well-known Boise businessman and philanthropist) founded the Donaldson Home for the Aging in the early 1900s, one of the first of its kind in Idaho. Additionally, Mary helped found the Idaho Magazine, was an effective campaigner for prohibition, raised five orphaned children, and helped to found and promote a national women's rights organization. Dr. Donaldson continued to practice medicine well into the 1920s.