In 1977, Johnson saw a picture of Mother Teresa on the cover of Time magazine. After reading the article she felt a call to join the Missionaries of Charity in their work on behalf of the poorest of the poor. At the age of 19, Johnson moved to the South Bronx in order to join the novitiate as an aspirant. In 1980, she committed herself to a life of chastity, poverty, obedience, and Service to the poorest of the poor, taking final vows in 1986. While with the order, Johnson, or Sister Donata ("Freely Given") as she elected to be called by her sisters, studied theology at Regina Mundi at the Gregorian University in Rome, receiving a diploma in religious studies. While serving at the novitiate in Tor Fiscale in Rome, Johnson was assigned the confidential task of editing and revising the Constitutions, the governing documents of the Missionaries of Charity. For six years, Mother appointed her to serve in overseeing the formation of sisters preparing for vows. After falling in love with a sister and then later a priest, Johnson broke her vows and left the order in 1997.