T.S.
When she's old enough to be self conscious about leg hair, she's old enough to shave.
I'd get her an electric razor so she doesn't cut herself and doesn't need to learn to balance in the shower just yet, and let her do it.
I have a son, so don't have this issue on my immediate horizon, but he'll shave his face when he starts growing facial hair... I mean I wouldn't make him grow a beard while he waited for some arbitrary age cut off for shaving... so... why wouldn't I let a daughter shave her legs if she's getting toward puberty as well?
HTH
T.