Im really not too sure what to do i have never been in this position before and i am really concerned for my DD 7.

DD who is 7 years old has been exploring her private parts now for the last 3 years im told this is a very natural what we need to do as parents in teach her when and where, what is approprite and what is not so it really has not been too much of a problem.Yesterday my 2 DD's where fighting just the usually tussel then DD 3 yells for me and tells me DD 2 pushed her head into her fanny !! i was totally speachless DD 2 said it was not true and that she was just pushing her away. They both beleive that the other is lying ?? i dont know what to do i tried to calmly talk to DD 2 she cried acted defensivly, I asked her why did she do it ? she shrugged her shoulders then i asked her if she had done it to any one else or if someone had done it to her after much tears she told me a boy at school had done it to her in the play ground. I told her that this was wrong and he should not have done it then she takes it all back becouse she does not want to get him or her into trouble. I try to talk to her a number of times since then she tells me she does not want to think about it or talk about it,she had taken it all back and said none of what she told me is not true ?? i dont know what to do. Do i talk to the teach er or the principle ?
kath