This question comes up pretty often here. My daugher is now 10 1/2 and has been shaving her legs in one way or another since she was 8. She too has very dark hair and it just made sense for us. At first I did the shaving for her when necessary (for special events where she would be wearing a dress, etc.). Then she did it with an electric razor (no cuts - so easy). Now she shaves herself with a 3 bladed razor. She also shaves her armpits when necessary. She is mature and I'm told by her pediatrician that we should expect her period in the next few months or so. (the rule of thumb she goes by is about 6 months or so after underarm hair appears).
I should say that my daughter, although mature and developed, does not wear make-up or revealing clothes. She dresses fashionably but not what we would consider inappropriate. We are very conservative Christians. Not that that matters, but I just wanted to let you know that we understand she's still a young girl and the leg shaving was more a matter of personal comfort, not necessarily vanity or pushing her to grow up.
I also get her upper lip waxed as well as the space between her eyebrows (nothing else on the eyebrows until she gets a little older). She has very dark hair on her face and it really needed to be waxed. She is appreciative that we have this done for her.
Best of luck to you - and if your daughter wants to shave, please consider letting her. Not out of peer pressure, but out of personal hygene.