D.B.
Good for you. Of course your child is curious whether anyone else stirs it up or not, and that's a good thing. And it's not only possible that she's hearing things from other kids, it's guaranteed! At some point, they don't always want to come to Mom and Dad. I'd do a few things: talk to the health educator at the school, talk to the children's librarian (at your local branch and also the nearest large library, and talk to place that deal with teen pregnancy (your local Planned Parenthood, for example will be very helpful with prevention!)
Then I'd show her some stuff from the internet that illustrates how things are so manipulated. There's the famous video that shows how a young woman's body is manipulated (through make-up, lighting and pure photoshopping) to make her look totally different than she really is. There are books by models that expose the nasty business of body image, eating disorders and sex for sale. The more kids can see that what's in magazines or on TV isn't real, the more they can relate to what's on the internet being untrue as well.
The other things to explore are body image and sexual messages. What does it mean to value thinness, even unnatural and unhealthy thinness? What does it mean to expose one's body to the world. Muhammad Ali supposedly told his daughters that the world's greatest treasures are hidden - diamonds are hidden beneath tons of rock, rubies and emeralds have to be mined down in the earth, etc. You can google the rest of the quote. But the point is, if these things were exposed where anyone could get to them, they would have a lot less value. From there, you can enter into discussions about giving away too much too soon to a crush.
There are some good teen novels about friendship, things that last and things that don't, and so on - again, go to the librarians for the hot titles. There may be some movies you could watch together as a family. One great place to discuss topics is in the car. There's a finite amount of time (go for the 15 minute rides, not the 5 minutes ones!) , and the child doesn't have to make eye contact with you, but she can't walk away either. A lot of experts advise this time and location for the sex talks, relationship discussions, and so on. That might be better than more formal sit-downs.
Good luck!