"Side note - I really need to teach her how to clean" - yes. xD It's so important to respect what you own and other people's possessions. I was terrible when I was younger, until my step mother came onto the scene and effectively changed that for both my dad and I. Now I'm 29 years old and quite house proud about a place that's only temporary housing! I would have it no other way.

For all your hard work and for being a real star letting her have 20 people in the house, maybe she could return the favor by helping out with the housework some more or something? Could be something for next time. So like, maybe if she's all "can I have an army of kids over here to mess up the nice, clean house?" you could come back with, "only if you clean every iota of the place afterwords, until I'm 100% satisfied it's spotless." Slightly exaggerated version. xD Afterall, it's your house too.

By no means am I father, so feel free to completely ignore me. If I were, I'd probably be a pain, but then isn't that the job of a parent? Haha.

In hindsight, I wish I were more respectful when I lived with my dad. I was too busy being a kid, and a messed up one at that, to appreciate some of the things that I now do. Sometimes I go over there and have dinner with them, but afterwards I'll wash the dishes and clean the worktops; sorta my way of trying to make up for it.