It sounds like she's starting to be a bit more helpful. At least she isn't trashing your house like some CF guests do. But she sounds exhausting hosting people for more than a night always is and is not to be undertaken lightly!!
If it's the snarky comments mostly that upset you, please address them as they come up.
The whole "In British culture, it's seen as unforgivably rude to criticise when you are being hosted and looked after for free. And driven around" is a great idea.
It's non confrontational, you could add " I'm using up my previous AL to host you, I have little spare money and I'm knackered. So it was nice you cooked yesterday and can make your own way today, as we've spent quite a few days together , or I've run you around, & I have a million things to do that I haven't had a chance to fit in".
She can get a taxi home from train station if need be, if you are busy. And of course she can sort out using her own phone. She's saved a ton of money staying at yours.
You've been lovely, but don't say yes next time when someone invites themselves to stay at yours. It's a great life learning experience that you can pass onto DSD too. "That's not possible" is always an acceptable answer, "...but I can send a link to hotels or b&bs in our area".
You now know how hard it is to host people on their holidays now, who can easily slip into expecting you to become their chaffeur, cook, hotel maid, entertainer and tour guide.
Far better to let them do their own thing and meet up or invite over for dinner, once or twice, in the week.
It's different if it's family or close friends, that you regularly stay with too. Reciprocal kindness is lovely.
Ps. You have a place to stay for a week in Australia now OP, start planning your cheap ticket..! 