Can’t recall too many specific details, so some statements may be incorrect. The movie begins with a girl probably in around her twenties on a bus to return to her old hometown. She goes to stay in her old house (?) which is currently being lived in by a man who knew the girls mother (can’t remember the relation), and this mans daughter.
The young daughter of the man believes that there is a monster living within the walls of the house, and the movie ends with the daughter finally killing the ‘monster’.
At the end of the movie it is discovered that this ‘monster’ was the mother of the girl in her twenties, who was believed to be burnt alive, but had in fact survived and the man living in the house had been rehabilitating her and caring for her in a secret room inside the house.
The movie was in english, released around the early 2000’s, in colour. It is not “the Uninvited”, which is suggested whenever I try to search for this movie.