Outstanding movie. Intelligent, beautifully shot and superbly acted. As a metaphor that's also open to your interpretation, it reminds me of the brilliance of The Babadook.
As someone with a parent with dementia, I can relate to the way the movie portrayed both the suffering of the grandmother, and the subsequent confusion and hopelessness endured by loved ones of someone with dementia. I found the ending quite profoundly affecting.
As a side note, I have had a good laugh at the negative reviews. They need to come up with a rating system so that stupid people know not to watch certain things. One review complained that the movie 'didn't explain things'. Yeah, that's the point. Sometimes you have to do your own thinking, regardless of how much it hurts, lol.