I am trying to find a movie that I watched on a streaming site not too long ago. It is about a young blonde woman who gets a job being a nanny for 2 rich spoiled kids, particularly a cruel teenage boy that torments her. She sees a ghost that is haunting them. She leaves after visiting her mom (early in the film) in a mental institution.
The ending (if you think you've seen it)
shows her going insane, and the ghost is all in her imagination.