I cannot deal with the "helpers"; I would really rather they not touch my stuff. I will clean up after the party.
I have also had someone put one of my good knives with wooden handle into the dishwasher, and I didn't notice until after I'd run it. It wrecked the wooden handle. I have had someone make a dessert (it was a potluck) at my place and used my nicely seasoned cast iron pan to make some kind of sticky, sugary reduction, and then scoured it with a soapy scrubby. My mother has always managed to chip a dish no matter whose home she is in. Growing up, I always got the blame for chipped dishes ("you have to be careful! I've only had these dishes a few months and already most of them are chipped!!") but as an adult I have noticed that I can keep the same dishes for 20 years without ever suffering a chip, while she is constantly replacing hers and most of them are chipped after 6 months. She also does a horrible job of washing dishes; most of the dishes she washes still have a greasy film on them after she's done. I do not want her helping.
I agree with this suggestion:
"Sally - I am serious. I am not trying to be polite by telling you to go back to the party. You need to stop."
Because I'm also inclined to think Sally is interpreting the OP's "no" as, "No, really...I insist....you don't have to do that....oh you are too kind, but don't feel you have to...."