Here's another script for making it all about you: "I'm actually pretty territorial about my kitchen, and we've got procedures that other people don't know about. Please don't."
And if they persist, "Maybe I wasn't clear; I'm sorry. I like to be the only person who does those things in my house, because I am picky." And if it really comes to it: "Please don't interfere."
Because it is actually rude to insist on cleaning up for someone else. The first offer is fine, but after that, Aunty is being rude to persist.
I've thought about this--it hasn't come up yet, but I can see that it could, if the right (wrong?) person was visiting me.
No one outside the family is allowed to cook in my kitchen, because I have celiac. And I'm not going to have someone use the wrong pan, or make something unusable.
I've figured I'd say, "We have rules in our kitchen because of my celiac, so you're not allowed to cook or clean up--sorry!"
At Thanksgiving, I like to use my nice china for the 16 or so people who come. We refuse to do much dishwashing that day--we'll do it tomorrow. That means that we have to be relatively careful about handling, because you can break stuff if you stack it w/ stuff between the plates, etc. And we need to keep it consolidated.
We've had to say, "Leave it to us, please," in a brooks-no-nonsense tone. It bothers my MIL, but I had to say to her twice, "This is my house and my dishes; leave this to me." I may have even said, "Please don't interfere," and maybe even once "I'm sorry if you don't approve of how I'm handling my dishwashing chores."
She called me before the last Thanksgiving I hosted to say that I didn't need to use china, I should use plastic plates. Because of the washing up. I said, "I'm the hostess, right?"