Kids! They want to be grown-up so fast, they can't wait to take their time a little, but then, did we?
Children do mature far earlier these days, and the advent of mobile and net communication is a two-edged sword as you are finding out. These texts may be just bravado, but you need to make sure your daughter knows the facts about sex, and its consequences.
Why not wait until you are having some quiet, private time, and broach the subject then? I told my three girls that I was available to tell the truth about anything they wanted to know, and if I didn;t have the anwer, I would find it and let them know. My youngest wondered if smoke comes out of a penis after ejaculartion!
So, be there for her when she needs you - explain that sex is part of being a woman, but it has its context, and is not something to do 'because everyone is doing it'.
This is a confusing time for her, as her body changes, and she hears all manner of nonsense, so be the oasis of calm, and support, and she will get through this - promise!