You say she doesn't have cable? Sounds like that's the reason she comes over mostly? So couple that with being messy while eating and it sounds like something is going on, whether it's a spectrum thing or she doesn't care.. Like others said, how much are you willing to give?
I'm all for being polite to people, but if they continue to encroach on personal territory, etc, then that's on them. It's like the no shoes on the rug. If you have to respect that, and she gets testy about it, be the same way while eating. Don't be afraid to do it, it's your house. All you're doing is giving her the same respect she gave you, at her house, concerning her carpet.
That's the language she speaks from what it sounds like. Just do the same in turn, and I'm sure she'll understand.
This reminds me of when I was younger. We had a guy living next door. Daughter long gone, wife passed years ago, pretty old guy. I believe his favorite activities was 7 and 7 and watching tv.
Anyways, the guy would wander around our block, walking through yards, etc.. Sometimes you might close the curtains because he would be there staring in lol... Not creepily I don't think, but old guy bored as hell.
One day he came over and was knocking on the door. I almost didn't answer it because I was so tired of him. I mean, it was just beyond annoying. (and I was still a young punk)
Anyways, I answered the door. He was all dirty, and started saying something, I think he was kinda drunk, but I was able to make out, "help me, my house is burning". :|
Yup, sure enough, he started a fire in the kitchen, the house was burning. Called 911, didn't lose the house but the kitchen needed a remodel. After that I believe his daughter put him in a home.
Anyways, even when you find yourself completely fed up with someone, don't hold onto that, because that could be the last thing you ever do to/for that person.
But the above lesson doesn't have anything to do with being or not being, blunt as hell. :)