The movie implies Caroline and Sitting Bull had no connection prior to her arrival in Standing Rock, which is inaccurate. They began corresponding around 1888, after Sitting Bull was in Washington, discussing fair prices for Dakota land and maps of the government's plans to reduce the size of the tribes' reservations at length.
The movie states that Caroline Weldon was a widow, which is inaccurate. She was married to Bernhard Claudius Schlatter, and left her husband for another man, with whom she had a son. She reportedly took her son with her to the Sioux settlement to meet Sitting Bull and live among the native Americans. She eventually got a divorce in 1883.
In 1887, the Dawes Act was passed, and residents of the Dakota Territory tried to pressure the Sioux people, who lived on land they wanted to occupy, to move to a reservation. When Susanna Faesch heard that Sitting Bull, leader of the Hunkpapa Lakota Sioux, was opposed to the plan, she began to write him letters. In 1889, Susanna, being a divorced single-mother of an illegitimate child, a social outcast, and legally unable to remarry, took on a new identity as Caroline (Catherine) Weldon, and moved with her son to Standing Rock Reservation to become Sitting Bull's secretary/representative. She began to try to organize his supporters in the area to oppose the Sioux Bill. Local newspapers vilified Weldon as a harpy who was in love with Sitting Bull and called her his "white squaw." During the time Weldon was with Sitting Bull, a religious movement called the Ghost Dance swept through the area. Caroline warned Sitting Bull that siding with the Ghost Dancers would turn him into a target, but he ignored her. She began to advocate against the dance, causing a rift with Sitting Bull, and finally, she left the reservation.
Though Sitting Bull's death is not historically accurate in the movie, it is portrayed with the sense of many native Americans, who often state that his death was a betrayal of the US government to a political leader.
Weldon, born in Switzerland, had originally been named Susanna Faesch. After relocating to Brooklyn, New York, she left her husband for a married man with whom she had her only child. After her lover abandoned her, and her divorce from her husband was finalized, Susanna changed her name to Caroline Weldon. With her son, Christie, in tow, she arrived at Standing Rock Reservation in 1889 where she pursued her dream of living among the Sioux and fighting the U.S. government for Native American rights.