J.R.
R.,
My daughter is only three, but I already get anxious thinking about the "boy" stage.
I think you are taking a good approach. It is so important to educate her on the facts without going overboard on details too early. But at 10, she's going to be learning everything from her schoolmates -- right or wrong -- so it's better for you to be ahead of the curve.
Does she like to read? I think there's an American Girl book on preparing for changes, what to do in certain situations, etc. Help her to think ahead to how she might respond in a certain situation. Perhaps you can bring up a topic in the news (like a teenage celebrity who just got pregnant) and ask her opinion. Don't judge or offer too many insights, just keep the guided communication going.
Can you get her involved in other groups that may offer some healthy structure and feed her self esteem? What are her hobbies and talents? The better she feels about herself, the less likely she is to succumb to peer pressure. If she has a flair for drama, maybe encourage her to try out for a play. A volunteer activity can also broaden her horizons and give her something positive to talk about with friends. Just get her involved and keep communicating.