I have a college-aged sister who is about your sister’s age. She also grew up in a rather odd household–very spoiled, on the one hand, and very neglected on the other.
I helped her move cross-country for better educational and career opportunities when she was 18. I hadn’t spent much time with her in a long time before that; there’s a big age difference, and I left home permanently at 18. I was, frankly, horrified by what I saw.
I had, as I mentioned, driven across the country to pick her up and move her here. Once I got there, she proceeded to show up about 4 hours late (?!?!!) to the rendezvous because she had decided to hang out with her friends for a while first. Didn’t bother to call me to let me know what was going on, either. Then, as I and some family friends loaded her stuff up, she didn’t so much as say thank you for coming or apologize for being so late for no good reason. She did, however, mention once we got to my house a day later that she expected me to lend her a fairly substantial sum of money in order to get some supplies that she needed by a certain time. I was surprised by this, and generally annoyed by all the previous shenanigans, so I asked what was going on, at which point she made a “talk to the hand” gesture.
I blew up. I should add that I was also about three months pregnant, so I was exhausted and queasy, and that on top of a hellacious drive did nothing to improve my mood.
I told her quite firmly that I didn’t allow anyone to treat anyone like that in my house, and that included me; that her behavior over the last few days had been totally unacceptable (I mentioned specifically that if she ever showed up 4 hours late for anything again without a seriously good reason, I wasn’t going to be there), that basic courtesies like “please” and “thank you” are to be used while under my roof, and, lastly, that one simply does not demand that other adults lend one large sums of money.
(In her defense, all of these behaviors had been modeled for her by our parents, but that still doesn’t make them acceptable, and it was past time she figured that out.)
She stormed out of the house, and didn’t come back for a couple of hours, after which we sat down and talked, laying some ground rules: courtesy, mutual respect, and so on. She didn’t like it much. I also lent her the money she needed with a repayment plan in place, which she followed to the letter.
Things were a bit tense for a couple of months, but it sorted out eventually, and she even sent me a text a couple of Mothers’ Days ago, thanking me for the kick in the behind that I’d given her. She has also significantly matured since, and while I certainly don’t claim all the credit in that department, I suspect that having someone tell her the plain facts of life may have helped somewhat.
Long story short, having a talk with your sister (perhaps a bit less bombastic than the one I had

) may actually help her. Leaving aside anything else, with the food thing you don’t want her to be that person at the dinner portion of a major interview who makes a rude face and complains when the company interviewing her takes her to one of the best restaurants in town. She doesn’t have to like every kind of food out there; few of us do. It will well behoove her to learn to be polite about it, however.