From CNA:
St. Margaret Mary Alacoque — whose feast day is celebrated in the Catholic Church on Oct. 16 — was a French nun responsible for spreading the devotion of the Sacred Heart throughout the Western Church.
Born in July 1647, Margaret had a great love for God from a young age. Her father, Claude, passed away when she was 8 years old. From ages 9 to 13 she suffered a paralyzing illness. This, in addition to a struggle over her family’s property, made life difficult for Margaret and her mother. However, it was during her time suffering with the illness that she made the promise to enter religious life. For some time during her adolescence, however, Margaret forgot about her vow and lived an ordinary life. It wasn’t until she had a vision one evening at age 22 that her life changed.