Not YA, or a book, but one of the Liaden short stories, available free here (http://www.webscription.net/chapters/1587872145/1587872145___3.htm), includes a character who has some form of (I think) bipolar disorder, and I think he's treated well. He's actually the 'saviour' for the main character in some ways, making her see that her life doesn't have to be bound by the strictures of her culture, especially since she's been rejected by what should have been her main support in that culture.