A lot of times people associate masturbation at any age with what it means when you're older- something sexual. But hey, when you rub yourself down there, it feels good! This is true at any age. If your daughter has discovered it feels good, then you totally have the oppurtunity to let her feel good about herself and exploring her body (not her sexuality, just how her body works) at an early age. So many people think that the more you know about your own body, the more likely you are to go out and share it with other people, but this is not the case. If your daughter knows that not only can she come to you with questions about her "private parts" but that you will talk to her in an open, loving manner, she's gonna be more likely to come to you and talk to you about what's going on- including getting her period, starting to like boys, and even (gasp!) sex one day. You've got the perfect oppurtunity to let her know she can talk to you about anything, thus greatly dimishing the chance that when she does have questions about sex, menustration, and the like, she'll come to you to get accurate information instead of turn to her peers who will tell her who knows what crazy things.
Please, be open with your daughter. One of the things I never had with my mom and dad was an open, honest line of communication about sex and the body. I wasn't even allowed to go to sex ed in 5th grade because my mom said "if you have any questions we can talk about them" which never happened. I was by no means a slut when I was a teenager, but I would not have gotten myself in quite so many precarious situations if I had the proper teaching about sex. I lost my virginity at 18 to the WRONG guy (tho, thankfully, there were no negative consequences afterwards, other than regret) because I didn't want to be a virgin when I went to college. I wish someone had told me in more than just an abstract way that losing your virginity can be a big deal.
good luck
