I'll have to join Anna in the angst. Seeing as guitar is taken, plus I can't play very well (read: at all) or sing. Back-up vocals might still work, but I'm afraid... Nah. If there's anything I could do though, I'd love to.
If my sister were older, I'd definitely HAVE you make her play piano. She's nine, and plays the piano like a little goddess. She's never gotten any professional teaching at that, she's just a natural at it. And drums... It kind of bugs me knowing that if she keeps at it, she'll be as good as Yoshiki at both when she grows up. But yeah, off-topic...