How can I tactfully tell my by-marriage niece I'd rather not have her come for my garage sale?

My niece is trying to clean out the estate of her mother - my sister-in-law. I live in a well-traveled and affluent area about 10 miles from her. She knows I have garage sales from time to time and she's been hinting around by email that she like to come over when I have one. I did have a sale Friday and yesterday, but I deliberately did not invite her. Reasons - #1 - she would bring junk to sell which detracts from my sale (I've seen what she trying to sell and it's just trinkets and dust catchers that nobody wants), #2) her house is filthy with cat waste and I don't want people coming to my sale and think that odor is coming from MY items. #3) I would have to feed her at least lunch while she was here and probably have to help her set up and knock down her sale. In general, it would be just too much trouble for me, being in my mid-70, to have her here. It's more than I can handle to have my own daughter come and bring her salable items. She's not even my blood niece, my late husband and her mother were brother and sister. I want to know a firm but tactful way to tell her "forget it."