Girl moves in with grandma with Alzheimer’s?

I remember watching a movie a while ago (pre-2010) where a little girl goes to stay with an older woman (I think her grandma, but not 100% sure) in her picturesque little cottage in the countryside and/or by the coast. The grandma starts developing some kind of dementia, and we know this because she starts repeating a story about how she made a friendship pact with a friend many years ago and they both pricked their fingers with a needle. That’s the only detail I remember!