Reading the other reviews I have realised I have a totally different oppinion about the end of the movie. It is not confusing and not an open ended movie. The dad said 'you have no idea how many things I have done to protect my wife/marriage' which to me means he had to kill his daughter for her not to tell mum about him abusing her. He was very convinced that the old Michelle is not his daughter because he knew she is dead.
When Michelle has received the gift from 'granny', her now husband told her 'you need to tell her the truth' which means 'you need to tell her you are not her missing daughter'.
Anyway, not a good movie at all with all the keeping Michelle locked in that room to realise and remember that actually they are her parents. Not a good idea to keep a close relationship with an unknown crazy lady who forced you to stay in her house and who killed her husband.
Waste of time.