I know we need to worry about boys safety, but I think what Disneyphd was trying to say is that there has to be a line drawn about when it is inappropriate to take boys to girls restrooms. That is why I think every public place should have family restrooms. Honestly, in the situation of the OP I wouldn't feel comfortable letting a 12 yr. old go into the restroom, but I probably wouldn't be taking a 12 yr. old to this concert, but I know we can't avoid all situations like this.
Also, I didn't feel like you were being disrespectful. I was trying to explain to you how little girls feel about these types of situations. It doesn't matter how many times you explain to them why the boys are in there, they still feel all icky. And yes, I do tell my DDs "to get over it", but it doesn't stop them from feeling this way. Also, some 9 yr. old boys think my 9 yr. old DD is quiet cute.
The boys know the differences between boys and girls and think at that age they should stop sharing restrooms. But, if an emergency, take the boy into the stall asap and go directly from stall to the exit and then it probably won't bother anyone, except the 9 yr. old girl.
Also, I didn't feel like you were being disrespectful. I was trying to explain to you how little girls feel about these types of situations. It doesn't matter how many times you explain to them why the boys are in there, they still feel all icky. And yes, I do tell my DDs "to get over it", but it doesn't stop them from feeling this way. Also, some 9 yr. old boys think my 9 yr. old DD is quiet cute.

