I don’t remember a lot of the details, I think I read the book about 20 years ago.
The main character was a girl, sent off to some sort of boarding school, which I think was run by her aunt and uncle or something. The odd thing is, I don’t really remember there being other students in the story, so maybe it was a former boarding school.
At any rate, there was a dollhouse in the attic, and if I’m remembering correctly, the dolls turned out to be just miniature people - living, breathing etc. The girl split her time between being miserable with her life and being obsessed with the dollhouse.
(Why do I remember this crap: It was in reading this book that I first learned the words “behoove” and “oblong”.)