Context for this story: I (M24) live at home with my mother and stepfather. My sister (F18) has always had a gripe about dishes. In our household, one consistent rule is that the person that cooks, doesn't clean. This applied a lot in our younger years, so whichever parent made the big dinner didn't get stuck with the dishes. This changed when my sister came of age and had a car. She often would eat out, despite consistent offerings of dinner and food at home. This is where the issue begins. She has taken issue with the fact that even though she didn't cook, she didn't eat either and felt she shouldn't have to do dishes. Often this lead to alternating dish days between my sister and I. I would unload the dishwasher, she would reload, or vice versa. I believe it was somewhat fair because she still had the obligation to contribute to the household she lives in. Fast forward to today. My sister has recently decided to undergo a major diet for bodybuilding. This means she no longer eats dinner with us, and does all her own cooking for her strict diet. However, cleaning has not been so clear. There have been a fair few times where she has made a sink full of dishes from meal prep and asks for help with them. Once in a while, no problem. But it's starting to feel constant. Just about every few days, she is asking for me to do dishes. Mind you, I cook about 50% of the time in our household, so per year olde rule: "Thou who cooks does not clean." This is not holding as true these days. Where I take issue, is that while the parents and myself make dishes, my sister does so at either a similar or higher rate. I feel that now rules should change, as the original intention of our rules doesn't hold. I think it would make sense and be fair for any dishes myself or the parents make to be our responsibility, and hers her own. She has constantly said no, and that "she's on a strict diet, working out 4 hours a day, and is tired". While I understand she wants help, I do not want to do all of her dishes before she gets home at the end of the day, since I had no hand in making them. She thinks otherwise. As a result, I've told her off and gotten in multiple arguments over it, because she made a decision to do a diet, and I shouldn't have to change how I live in the household for just her. AITAH for not wanting to do my sister's dishes?