So, based on this post, we've now established that as far as you're concerned, only women are entitled to privacy in the bathroom, predators only prey on little girls (and little boys are never molested or targeted), and women are certainly never predators (and as such you never have to worry about what will happen if some strange woman is in the bathroom with your daughter).
Ultimately, a person could try to just say they're "transgender"... but if they want to actually use that as a valid defense, they'll have to be willing to go to court, at which point unless they can present some evidence to show that this is more than just a ploy, it's going to fail.