Fragile by Jaume Balagueró
http://imdb.com/title/tt0422272/
I have ONE reccomendation for your mother, and I am 100% sure that she will love it. It fits everything you listed spot-on, EVERYTHING. I cannot stress this enough - both of you, sit down together, and watch it. It's severly underrated.
A heart-warming ghost story with stylish direction, and intelligent writing. A twist that you will not see coming... and of course, even if it leaves you with a smile on your face and a tear in your eye... it still packs a level of tension and fear throughout the film that is essential to all horror films.
Rated PG-13 for intense sequences of terror/violence, and some thematic elements.
You will not regret renting this movie for you, or your mother. It's excellent.
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Try: The Others and Kairo (not the American 'Pulse' - even though I did enjoy that as well)