I believe my mom was 14. I was 13. My oldest daughter was 13, and my babies (now 14 and 15) were both 10. Interesting, huh? The babies
were from a different father, and I know his sister had her period when she was 10, so I figure it was his family genes in them. Who knows?
Genetics, evolution, fast food ... I don't know. But I've always been very open with my girls and it's worked well for me, so far. I'd advise you to talk with her about anything she seems willing to listen about. I started talking in very general terms just to let them know I was available for anything. All I knew was that I did not want them to learn about sex "in the street" as I did, which is probably why I became sexually active so young.
Don't be afraid, but take cues from her. She'll let you know what she's ready to hear. And although it does seem a little scary at first, it opens a whole new bond and will bring you even closer to your baby.
Enjoy it.
By all means, don't let go just yet! She needs you more than ever during puberty.