Red Deer by Aimee Lamb

When her convoy is attacked and everyone massacred, a young French girl, Anne, manages to flee across the unknown praries where she is later found by scouts from a Mandan hunting party. Taken in by the tribe, Anne, who is given the name Red Deer by her captors because of burns sustained during her flight and her red hair, must learn their ways and language in order to survive. Life is hard but good until the smallpox epidemic almost wipes out the Indian tribes. Surviving, along with a few others from her Mandan family, Anne finds love in the arms of a Pawnee warrior and must decide, when her brother Pierre finds her and tells her their mother survived the massacre, whether to go live among her people, or to stay with her new family.