Yes, you ARE insecure as a parent. I just read and answered your question asking if your child is gay.
You would be well served taking a parenting class. Please look for one at your local community college. Ask the school guidance counselor for suggestions. You REALLY need some help navigating teenhood. If you don't, your daughter is just going to be more and more embarrassed by you.
You also need to make sure that you have your daughter's password to FB. You need specific rules for FB in order for her to have the privilege of being on it. You should NEVER write on her wall. Ever. She will NOT like that. Even my 20 year old doesn't like it, but because he's a "man" now and I'm paying for his college expenses, he has to put up with a comment from me ever so often. When he PRIVATELY messages me asking me not to write, I simply write back "I love you anyway..." However, your daughter is NOT 20. Don't write ANYTHING on her FB.
The reason you need her password and the reason you need to look at her facebook every day is because you want to head off any trouble right away. If she were to post inappropriate pictures or if any of HER friends post inappropriate pictures, you need to know. Don't talk to her about any of the silly, inane, and just stupid stuff these girls talk about. You just want to watch out for her safety and all of that.
Since she does sleepovers with her friends, you need to have these mothers' phone numbers and you need to be calling the mothers to verify that it's okay for your daughter to sleep over. The reason is so that you actually know from the parent that your daughter is where she says she is going to be. If you start this NOW, she'll be used to it when she is 15 and won't be screaming because you "all of a sudden don't trust her".
Your daughter WILL be sneaky once in a while. That's her JOB, to see how far she can push the envelope. That's what teenagers do. Their brains are NOT developed enough to really understand the gravity of their actions. So yes, they push the envelope and sometimes act irrationally. As the parent, this is what you have to help her navigate with structure, understanding, an amount of strictness, and LOVE. If you leave love and understanding out, you will shoot yourself in the foot, making her resent the heck out of you and try to be even MORE sneaky.
Your daughter is no longer a child. She is a teen. Treat her with respect, but don't act scared of her. I think that if you take a parenting class, you will have much better perspective. And you won't be talking to her about stuff that pushes her away from you, like you are from the other thread.