How odd. Obviously if you're at someone else's house, it's polite to ask if it's alright to use their bathroom - I even do that at my best mate's place, just because I'm stupidly polite, to the extent that people often say 'No' when I ask to do/get/borrow something just because they know I'll be like, 'Oh, ok then'!), and it's normal to say 'Just popping to the loo' so they don't just think you're wandering off, but if she does it when you're not at your house and she actually asks your permission to, literally, pee, rather than just ask if she can use your toilet, that's weird!