"In 1922, Dr. Cushman accepted an appointment as a medical missionary from the predecessor of the United Board for World Ministries. She was 52 at the time, and her mission was to establish a hospital in Chilesso, Angola, West Africa, which she accomplished." (source)
I was introduced to Mary Cushman through the book compiled by Nina Millen entitled "Missionary Heroes." In this book we learn about how Dr. Mary worked in the hospital and had a good relationship with a little black girl named Vikomo. This little girl ended up being big help as she worked among the people.
Dr. Mary worked among Vikomo's people for 20 years. By the time she left, Vikomo was preparing to go to Portugal to learn to become a doctor. Her plans were to become the next doctor in Dr. Mary's Hospital.
The story of her life is published in a book called Missionary Doctor.