Oh if only he knew that she did it because he was amusing, not because she knew something. That was just a happy piece to the puzzle. "Nice people? Oh by that logic, you wouldn't let yourself in here. Or half the people on this ship." Not that she thought he did such a thing, but still. "I haven't actually come in anyway." Yes it was childish, but so was the equivalent of 'I'm not touching you' which she seemed to be playing.
No it wasn't her business, she knew that. It still made her curious though. She would have to keep an eye on that. "Ah no, none of that on this trip. If I do something like that, I know I'm being kicked out of the TARDIS first thing. I don't really want to be kicking and screaming into space." Anyone who got booted out of an airlock wasn't going to last very long. Except maybe him.