Rhodes was born as Mary Ann Dormer in South Lake, north of Gananoque, Ontario on 12 August 1882 as the eldest child of John and Annabelle Dormer. She had two younger sisters, Sarah and Eva, and they attended the county school one mile from their home. When Rhodes was 18, she enrolled at the University of Guelph, specifically the Ontario Agricultural College, to take a course in home economics.
In 1912, Rhodes married her husband, successful Seeley’s Bay farmer Victor Rhodes, and they had one son, Murray, in 1916. Her son later became a dentist and had his own Kingston, Ontario practice. Rhodes was a lifelong member of the United Church and was the church organist for many years. Her husband died in 1954, and she lived in Seeley’s Bay until 1968.
In 1986, Rhodes moved into a nursing home in Kingston. When she was 109, she was chosen to present flowers to Princess Diana when she visited the home. She enjoyed reading poetry, particularly the works of Lord Byron, Robert Burns, William Wordsworth, and Henry Wadsworth Longfellow.
Rhodes was confined to a wheelchair as a supercentenarian but was still mentally sharp at 115. Longevity ran in her family, with her father and sister Eva both living to their late 90s. She had three grandchildren and several great-grandchildren. She died on 3 March 1998 at the age of 115 years, 203 days, being the retroactive seventh-oldest person ever at the time of her death. She is still the second-oldest Canadian in history.