How motivated is she? My wife and her ex-idiot were both instructors, so they figured their kid would be a natural. She's 12 and has been a cert for ayear, but I have NO confidence in her scuba skills and have to watch her like a hawk when she dives with us.
She can take diving or leave it - and if it's not done for her, she won't do it. We have a dive boat, all teh gear in the world, and she HATES to go out on it - not when she could be on Neopets or Gaia.
When I was 9, I taught myself to dive and lived and breathed diving from then on no one had to watch me or worry if I knew what I was doing.
So if your kid is psyched, pumped, and ready to go, more power to you. There are a lot of similarities between teaching kids and adults scuba - they get it or they don't. If she gets it, great; if not, oh well.