Unless there is no door on the bathroom, she wants you to see her and experience everything else that goes with that. Most people try to bump into the person in the grocery store or gym in your case, but she definitely has her own style. She started it, and you have every right to ask her what it is all about. If she says it was nothing and that you are making a "big deal" out of nothing, then maybe ask her if she does it for the mailman too. I know that I don't invite people in and then jump in the shower with the door open. No free shows here. How about you, do you do that when you invite people over? Maybe we are the only two, but I doubt it. Have some fun with it and ask her questions, putting her on the spot the way she did it to you. You sound like a decent person, don't let her jerk you around.