Sarah Riel the sister of Métis leader Louis Riel was born October 11, 1848 in St. Boniface, Red River Colony (now in Manitoba). She joined the Grey Nuns as a novice in 1865 and in 1868 became the first Métis Grey Nun from Red River. She could speak English, French, Cree and Michif and in 1871 was sent to Île-à-la-Crosse where her father Jean-Louis Riel was born. She served in the school and the hospital of the mission until her death of tuberculosis December 27, 1883. She took the name Sister Marguerite-Marie in 1872 and is buried under that name at the cemetery in Île-à-la-Crosse. Her headstone in French reads: Ici Repose Rév. Soeur Marguerite Marie (Riel) Decédée 27 Decembre, 1883, Agée 34 ans, R.I.P.
She and her brother Louis Riel wrote to each other and letters remain describing their relationship and her life in Île-à-la-Crosse.
On April 27, 1885, the day after the Green Lake Post was looted during the North-West Rebellion, the Grey Nuns of Île-à-la-Crosse, terrified that Riel who had accused them of letting his younger sister die in misery would seek revenge, fled the village along with most of the personnel and dependants of the Hudson's Bay Company Post and the Roman Catholic Mission. The large group camped on a small wooded island north of Patuanak until the crisis was over and returned to Île-à-la-Crosse on May 29.