I read it years ago, and haven't been able to find it since, but I only have a vague memory of it. I think it was about 3 books long.
I think it was about twin sisters going to live in a boarding school in the middle of the forest. A scene that stuck was when one of them was wandering around at night and saw throw a small window in a door a striking image of a woman's face in a painting. I think the overall story was that some ancient spirits from the land were haunting the place or something along those lines.

The Dreaming?

Yes it is! Thank you so much