Mary Schweitzer was born in Pittsburgh, Pennsylvania on May 23, 1860. Both of her parents were born in Germany. Mary entered at Clyde on July 23, 1904, after caring for her aged invalid mother until her death. She was invested on February 21, 1905, and made profession as Sister M. Rosalia on March 10, 1906. Perpetual vows were made on January 13, 1912.

Sister was small in stature, but an energetic, capable worker, and though mature in years, was very childlike and docile. She had a good voice and rendered the hebdomadary parts of the Divine Office very beautifully, in her earlier years at Clyde. For many years Sister operated the folder in the Clyde printery, when work was heavy with both the English and German editions of "Tabernacle and Purgatory" and a large assortment of booklets and leaflets. She was assistant Novice Mistress for a short while, and also spent some time at Mundelein.

Sister was a humble, quiet, charitable person. In later years when her eye-sight began to fail she volunteered for the Tucson foundation, where her prayerfulness, charity and community-mindedness made a valuable contribution to the community. She had become almost totally blind at the time of her death on January 27, 1940, at Clyde, in her eightieth year.