A. No, but don't be surprised by or mad at the woman who tells you to wait your turn. She's not required to let your child go in front of her. And your kid's pee dance notwithstanding, she may need to go just as badly.
To avoid the whole awkward conversation, you could try giving "the look." I find that sometimes, if you can catch a person's eye as you're telling your child, "Hold on, baby, hold on," you can have a complete conversation in one glance. And the line leader will likely motion you to the front.
If not, your kid may discover a heretofore hidden ability to hold it in. Here's hoping!