Your daughter is mentally getting prepared for the act of sex, and thank goodness you are a diligent parent and have caught her before she makes decisions that she is not 1) old enough to make and 2) could very well compromise her health.
As we get older, we should not forget what the surge of hormones can do and the lack of irrationality that it produces. This is the hard part for you as a mother: now that you are aware of what is going on and what she is mentally engaging (all actions are produced prior as thoughts), you have two extremes:
1) Do I put her on lockdown, take away her privileges and watch her like a hawk?
OR
2) Do I talk to her, hoping she will understand and try to guide her to the right path, while allowing her to control some decisions without extreme supervision?
The only one who can determine which option to take (or a middle approach) is you as the parent, because you know your child and love your child. I have a wonderful mother and could only hope to be half as great as she. My mother applied Option 1) with me, and I was horrible to her because of it (although I deserved it fully, but at the time I did not understand that I did).
I did not understand what was going on with my own body and was putting myself in situations that now (at 27 and with three step-children) am so grateful that she took the countless energy to make sure that I did not. Bottom line, however, was that I was that child that needed Option 1 and if you gave me an inch, I would take a mile. My mother knew that and was very strict. I remember her telling me once when I got grounded: "I do not like grounding you, S.. Never forget, when you are grounded, your father and I are grounded too. I assure you, it is easier to let you do what you want and not ground you. But I love you and you are grounded because I can not allow you to hurt yourself. You will understand someday." Of course, I would walk off in a hoot saying she was wrong, I would never understand, but when I reached the age of 24 I understood and I was grateful and I apologized. It took 11 years to appreciate and understand, but I did and my mother and I are very close now.
I believe, as a mother, the right approach is within you. You know your children better than they understand themselves, especially with hormones and everything altering their brains. The first thing to do is
1) decide which option or middle approach that you are going to tackle, and commit to it.
2) If signs of progress or worsening behaviors persist, alter your plan. With kids, everything changes as their hormones increase or decrease - what works today may not in a year from now-if your child shows signs up progress, reward it and vice versa. No one said a parenting plan does not have to change.
3) Be the parent. Giving the child what they WANT is not giving the child what they NEED. Remember, winning the WAR is the goal; not just the battle. Don't surrender and do everything with love. The child will most likely always fight, but that is why they are the child. It is the parent who makes the child become a successful adult who is able to have children of their own. As hard as it is and as mean as children can be when they are restricted, the more they appreciate it at the end. I am a living example and my mother is my hero.