Normally I'd advise a nine year old to wait until she got a bit older to start. My sister just turned ten and I gave her a very brief guide to shaving awhile back since she was curious. It's unnecessary for her to do it now though, so she's waiting 'til puberty.

However, if your daughter is starting to grow more hair than she feels comfortable with, then I suppose she could start shaving now. At that age I'd wonder if it might be a kid fad, and if she's being bullied then that's another area entirely that needs addressing. However, we don't all develop at the same rates and I know some of my sister's friends are already entering the early stages of puberty. So in your kid's case, I wouldn't be totally against the idea. It's really more of a personal thing at this point.