Johnson was born in Ann Arbor, Michigan, in 1958. The family moved to Beaumont, Texas when Johnson was 12. By this time, she was the eldest of seven children. In high school, Johnson was an accomplished member of the debate team and was voted "most likely to succeed" by her classmates.

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.

Since its inception in 2000, the A Room of Her Own Foundation (AROHO) has awarded six women with the biennial "Gift of Freedom Award," an award of $50,000 accompanied by creative and professional resources in support of the recipient's proposed creative project. Returning to its origins, the foundation also hosts a Retreat for Women Writers at Ghost Ranch every other summer. Johnson continues to serve as Creative Director of the foundation's retreats and to supervise the various publication contests and programs run by the foundation.

With the support of the foundation's growing community, Johnson finally published the story of her work with the Missionaries of Charity in her memoir, An Unquenchable Thirst: Following Mother Teresa in Search of Love, Service, and an Authentic Life (Spiegel & Grau, 2011). The book earned a place on Kirkus Review's Best Books of the Year list. Johnson continues to speak about the book and about her work with the Missionaries of Charity, and her decision to leave, with book groups and institutions around the country.