Teresa entered the Convent of the Good Shepherd at 17 years of age, receiving the Holy Habit on August 5, 1893 and being professed on August 8, 1895, taking the religious name of Sister St. John.
Teresa's older brother William was a carpenter who was hired to do some necessary work around the convent. So touched was he by the peace and tranquility of his sister's new life, that he left shortly after to become a Trappist monk himself.
In 1900 she was one of a band of five missionaries chosen for work in Mexico. Here she learned the Spanish she was fluent in for the rest of her life. After nearly a decade at this work, she was forced to make a dramatic escape to Canada at the start of the Mexican revolution in 1907. At the U.S. Mexican border she was forced to replace her religious robes with secular dress and to wear makeup for the first time.
Returning to Toronto, Sister St. John was named Mistress of the Magdalens. According to the Archivist of the Convent, "Her exuberant nature soon won the hearts of her charges and for thirteen years or so, she guided, directed, and consoled these dear souls through their many trials, temptations and difficulties, celebrating her Silver Jubilee with them."
She was named Mistress of Novices in 1932. Again, according to the Archivist, "She had great love and zeal for the Missions and inculcated this missionary spirit in her Novices. Naturally enough, her predilection was for the Scarborough Foreign Missions and as she became acquainted with the young Seminarians, through her Priestly brother's petitions for prayers for their perseverance, she would designate a certain Seminarian to each Novice to keep under her spiritual wing."
Like her older sister Johanna (Sr. Geraldine), she was a skilled artist but water colour, not oil was her preferred medium. Her beautiful floral borders grace some of her sister poems.
In 1940, at age 65, Sister St. John was retired from her charges and turned to Sacristy work in the laundry, mending, pleating and folding Sacristy Linens until eight months before her death at 86 years of age, after a lengthy illness. Shortly before her death, her brother Alex, who had left Toronto at the turn of the century to move to Chicago, returned to the city for the first time and brought his son, Gerald to meet her. Alex was so anxious to see his sister again that, when they reached Detroit where they had planned to spend the night, he refused to stop and urged Gerald to drive the rest of the way to Toronto. They drove directly to the convent, without even stopping at their hotel to change or freshen up. As a cloistered nun, Sister St. John was only permitted to greet them in a formal parlor. This was a major concession to modern tastes because, not many years before, she would only have been able to speak with them through a sliding partition. Alex memories of Teresa were of a fresh, young teenager on the cusp of life, and he was so profoundly moved by the toll the years had taken on his sister that he woke Gerald up in the middle of the night to return to Chicago after only one day's stay.
Over 14 priests served at her funeral including her nephew, Francis Carroll, the Bishop of Calgary, R.S. Diemert, the Superior General of the Scarborough Foreign Missions and P. McGovern, the Auxiliary Bishop of Toronto.