Good job on not escalating the situation!
I'm wondering though, could you have validated her feelings a bit in this exchange?
Her: Its weird that you are always in the bathroom when I call you. Why is it just coincidence like that?
Me: I don't remember that ever happening but maybe. If I have to pee then that's what I will do.
Her: Yes you are. Your always in the bathroom when I call.
Me: Ok. No big deal. If I have to pee that's where I will go.
The only part that I find invalidating is the "No big deal" comment. Although, I must admit that the questions did sound like baiting and you probably handled it really well with her.