SciFi and Fantasy Book Club discussion

Im searching for my daughter, who read a book in middle school, around 2004. All she remembers was the cover had the 2 children the book was about, the girl had spiky blue hair, and a dragon on it. In the book the 2 could change into dragons or other animals. She always talks about a quote from the book; "if a fish could raise an eye brow *insert character name* just did it" Was hoping to get it for her birthday, any help would be appreciated.

David wrote: "Im searching for my daughter, who read a book in middle school, around 2004. .."

I hope you find her!
(Sorry, can't help with the book.)