Simple fact is that once she starts with boys she will do it no matter what you say or do.
You can't lock her up in a tower to wait for her hair to grow.
They always find a way and the more you oppose it the more she will do it.
I hate the idea too ~ I was a boy once and I know what is going on but as far as the THW is concerned they invented sex. How she supposes she and her brothers got here God only knows. I did ask her once and she replied that it was "Too gross to even think about"
All a father can do is hope that the child has enough good sense to be careful and to remember all you have tried to teach her.
Other than that you are a free taxi service, provider of funds, and general facilitator of her enjoyment of being young ~ just don't expect to be listened to.