Sarah Hannah Roberta Grier was born in the Carrying Place, Upper Canada, to Rev. John Grier, a high church Anglican minister who had emigrated from Ireland in 1923 and been ordained in Quebec, and his wife Eliza Lilias Geddes. Hannah (as she preferred) was their third daughter and sixth child. Her parents took responsibility for her education at home, which also for a time was in Belleville. One sister, Rose Jane Elizabeth Grier, became a teacher, and ultimately principal of the Bishop Strachan School in Toronto. On July 23, 1859, Hannah married civil engineer Charles Horace Coome, who worked on the Grand Trunk Railway, and the couple initially lived in Kingston.
In 1862 Charles Coome accepted an engineering job in Britain, and the couple moved across the Atlantic. While in Britain, Hannah Coome became acquainted with the Oxford Movement as well as the Community of St Mary the Virgin in Wantage and felt drawn to mission work. She also became pregnant, but lost what would be her only child after a severe fall which also required a long convalescence.
The couple returned to North America in 1876, but a year later, Charles Coome died in Chicago. Hannah Coome continued to live in the American city with a nephew and a brother for several years, and supported herself by teaching Decorative Art, as well as by embroidering hangings and other decorations for churches.
Nonetheless, by 1881, Hannah Coome considered entering a religious community, especially returning to Wantage, England to join the Community of St. Mary the Virgin. Instead, at a party arranged by her sister Rose as she went to Toronto in 1881, Hannah Coome met Reverend Ogden Pulteney Ford (high churchman and priest at three parishes in Toronto) and Georgina Broughall (wife of the rector of St. Stephen in the Fields Church), who told her about their plans to form a similar sisterhood there in Toronto. The Canadian group also held an organizational meeting and others in the winter.
Thus, in June, 1882, Coome and Amelia Elizabeth (Aimée) Hare traveled to Peekskill, New York for two years' formation at the Sisters of St Mary, a relatively new Anglican educational and nursing order led by Harriet Starr Cannon, while the Canadian group did further fundraising and organization, including within the Family Compact for which Rose and Hannah Coome may have qualified. Hannah Coome and Aimee Hare trained with the American sisters in their hospital and social missions in New York City. Upon completing their novitiate, Coome professed religious vows on September 8, 1884 at the Peekskill motherhouse, and she and Hare returned to Toronto.