I don't remember much except a young woman travelled to a boarding school where she learned magic. Some mystery and intrigue throughout, and at the end of the book there was some sort of conflict that opened a rift in the world. I'm pretty sure it was referred to with the word rift, and it's possible that it was in a tower?
I've been looking for ages but don't have enough to do a proper Google search. I read it sometime before 2010, but am not sure how old it is. I'd guess UK or US as it seemed very Eurocentric.