I don't have a bipolar child, but I hear a lot of people mention the book, "The Bipolar Child" on this board. I have the book, "Raising a Moody Child" written by a psychiatrist who works at OSU hospital and it addresses both depression and bipolar in children.
I would keep a daily mood journal charting her mood and behaviors. That will allow you to identify a pattern as well as track what is working and what isn't.
Good luck to you.