Is it normal for an 11 year old girl to wet herself and not tell anyone?

I don't think that you have anything to worry about. That is an age when girls are changing so much physically, emotionally, and socially. Maybe she didn't think anyone would notice. It can be an embarrassing situation and maybe she didn't want to tell anyone. Girls at this age don't always have the social skills to deal with a problem like that, so they do what to us makes no sense.

Is this your daughter, student, friend? The best thing that you can do is open the lines of communication. Let her know that if she wanted a non-judgmental ear that you are there. Then validate any feelings that she shares with you by relaying how you might feel the same way if you were in that situation.

If this was a chronic thing, it may be another discussion, it also depends on your relationship to her.

Hope that helps, I'll be on if you have other questions.