P.G.
My co-worker just had this same situation with his daughter. He talked to her about the boys coming and suggested a Peter Pan theme or Neverland theme - I can't remember exactly. That way, they were able to have fairies for the girls and pirates for the boys, and ALL kinds of games based on neverland. I think they even had indian stuff, etc. Don't know if that will help, but if she likes Tinkerbell, she may go for it. Google may help you tons in this case.
http://www.birthdaypartyideas.com/html/peter_pan.html