H.W.
E., I'm going to chime in because I want to help.
Back in the day, when I was thirteen/fourteen or so, I was that kid you are describing. I was thirteen and it was more in the sending notes/private conversations category that I and quite a few of my female peers all were lying to each other about how experienced we were.
What you might want to address is *why* she feels the need to lie. By my freshman year in high school, E., there was a LOT of pressure to have sex-- or sound like you were. One couple who was having sex discussed it openly and seemed very sophisticated. No one even asked if they were using protection or anything. We, like a lot of kids, sort of thought they were cool for doing it and also sort of thought they were playing with fire.
We lied because we wanted to fit in. We had very little idea of what we were actually talking about. We knew what we knew from some books, some gossip-- but not experience. We were young, insecure, and hoped our lies would fill the holes in our lives created by pubescent insecurities.
Please start that conversation, even if it means going to a counselor. You got lucky-- she's only talking about risky behaviors now as a form of social attention-getting. Get some help but don't freak out. FWIW, I was a virgin until I had graduated.Sometimes there's a lot of talk which amounts to nothing.