I think this is about the 500th time I've seen this horror movie done.... So, an old lady, who is in the throws of dementia, and wheelchair bound, is looking to hire a caregiver (a nice young lady).
She shows up at the house, where everything seems OK, but the man with the 1 car just drops her off, and doesn't really say when he'll be back?? And when he does come back he's upset with how the young lady is treating the old - so he doesn't give her a ride.
As time goes on, the older lady becomes strong, can walk, has her memory intact etc. While the younger lady becomes weaker and forgetful.
In the end, you realize the person who was stuck in the old woman's body was also a younger woman who had come many years before. She is now free to leave, with her replacement officially installed.
RECOMMENDATION; SKIP! Boring, lame, and it's been done hundreds of times!