Sister Rosalie is a non-canonical character created for ITV's 2005 adaptation of The Mystery of the Blue Train. She is a nun in charge of a convent located in or near Nice.
After the murder of Ruth Kettering, Poirot searches her compartment on the Blue Train. Among the items he finds is a crumpled last page of a letter from one "Sister Rosalie", apparently to Rufus Van Aldin, promising to arrange something to his satisfaction. Poirot goes to the convent and learns that Sister Rosalie is the person in charge and that in the same convent was one Sister Dolores, wife of Rufus van Aldin.
Sister Rosalie is portrayed by Helen Lindsay.