Have you had the sex and baby talk with her yet? If not, she needs it now. I would talk to her about sex, babies, diseases and what it means to be sexually active (any act of sexual contact), why it is important to wait until she is older, reputation, responsibilities, morals, pregnancy, etc. Taking care of her body and mind and respecting herself and learning how to say no to boys. You don't have to talk to her about it all at once, just start asking questions and letting her talk to you about boys. Make sure she is supervised at all times. She should not go anywhere by herself. Always call the parents of her friends to make sure she is where she is supposed to be. Call the parents directly and not her cell phone. She shouldn't be in a room by herself with boys or by herself with boys period. She is 13 and shouldn't be dating yet. If you need help talking to her about sex, there are plenty of books out there. I don't think she needs birth control yet. just some communication with her and teaching her what is right and wrong. She is only 13. But some girls start really young, but if you talk to her about these things, I think you can have a powerful influence on her. Good luck!
Added: Having friends that are boys is different than dating. And should be allowed but with supervision. Boys and some girls are very interested in sexual things at this age, so she just should be aware of these things. Even if it just curiousity. Birth control is not something that should be taken lightly. It is medication and cause disruptions in normal hormone production. I don't do well on birth control pills. But I was on them throughout college. So it is something that should be discussed with her doctor. I personally don't reccommend it at this age, but perhaps in a few years.