She was always the sweet, shy one, and so paranoid of her acne, which she has had from a young age.

We tried to explain that it was an age thing, that if the 17yo was a boy, we would have done the SAME thing.

We explained we did it to protect her, we explained how 13yo and 17yo have different emotions and all the rest, but of course she didn't want to hear it. She just lays in her room in the dark not talking to anyone. I know it is not my job to be her friend right now, but to be her mom, but any advice would be appreciated.

One thing you haven't discussed very much in your account is your daughter's relationship with her other friend (the one who is aged 13 or 14).

I'm not sure what your attitude is towards friendship, but unless some obvious red flags are apparent there, I'd be inclined to avoid doing anything that might give your daughter (who is currently very sensitive about the interference of her parents in her relationships with her peers) any additional cause for resentment.

This may possibly involve giving her a sincere apology for breaching her trust or overreaching in your response to her relationship with her friend.

(Showing that you can be fallible in your parental judgment when your daughter is 13 [and is probably savvier than one might suspect] would be the honest thing to do, and I'm sure she would appreciate the gesture of your openness if you can convince her that your action is genuine.) I also invite you to consider your own motivations for acting the way you did more deeply.

We had to tell her that there is absolutely no way she can have sleepovers with the 13 year old and 17 old (which they were planning).

We've never fought with her in our life (she has always been so easy until now!

Were they mostly about you and your prejudices, or were they truly mostly focused on your daughter's well-being?