I'm From Nowhere, by Suzanne Myers

Wren's mother gets a once in a lifetime opportunity to work in Greenland, but she can't take Wren with her.  Instead, she enrolls her daughter at Hardwick - an exclusive boarding school.  The move surprises Wren because all of her life she's listened to her Mom complain about how awful that place was.  But within days, there she is with some hastily-bought cold weather clothes and a new Gibson guitar.

Being at her Mom's alma mater gives Wren an opportunity of her own to learn about her Mom's history.  And harnessing her detective skills, she tries to uncover her mother's biggest mystery -- who is Wren's father? But as she comes closer to an answer, tragedy strikes and a series of events unfold that teach Wren a lesson in the true meaning of family.

While plagued by some pretty crazy fantasy and a few glaring improbabilities, this is actually a lovely story.  The key is Wren herself -- one of the more no-nonsense YA heroines of recent memory.  She's far from perfect, but comes with great composure, refusing to be dragged down into dramatics.  The story is straightforward and free of angst.  Even the story's foil (a snooty bully) never really fazes her and the slight bit of romance is pretty matter of fact.