Rosebell was born on Oct. 5, 1908, to Cornelius and Mary Beatrice Head Smith of Bardstown, Ky. When she was 5 years old, her father died and her mother moved the family to New Haven where Rosabell began her early schooling. There, too, she met the Ursuline Sisters from Mount Saint Joseph who staffed St. Catherine School. After making a retreat at the Mount, she made her decision to enter the novitiate, as she had always wanted to be a Sister. Rosebell returned to Mount Saint Joseph on September 7, 1926. After a six‑month postulancy she received the Ursuline habit on March 19, 1927, and the name Sister Mary Cornelius.
Sister Mary Cornelius prepared for the teaching apostolate and began teaching the primary grades at St. Martin School, in Rome, Ky. For nearly 40 years, Sister Mary Cornelius taught either the primary or intermediate grades at numerous parochial schools throughout Kentucky. She also taught in the public schools at Raywick and Flaherty. In 1972 she was missioned to St. Angela Educational Center in Louisville to serve as the bookkeeper, which she did for six years. Sister Mary Cornelius then began her service in outreach work at St. Boniface in Louisville where she was seen daily in the Soup Kitchen. She was involved in various peace and justice issues, including marches with Right to Life in Washington, D.C. Her many efforts at St. Boniface continued for 10 years.
At the age of 80 in 1988, Sister Mary Cornelius returned to Mount Saint Joseph where she spent her final years. Sometime later she received a diagnosis of lung cancer which was too far advanced when she went to see the physician. Beautifully resigned in her suffering, Sister Mary Cornelius died peacefully on July 23, 1991. Her funeral Mass was celebrated at St. Alphonsus Church by Msgr. Bernard Powers who was also the homilist. After this Sister Mary Cornelius was laid to rest in the convent cemetery.
The chapel at Mount Saint Joseph underwent major renovation between July 1991 and July 1992. The funerals of all MSJ Ursuline Sisters who died between these dates were held at St. Alphonsus Church, St. Joseph, Ky.