If you have no restrictions on your amount of trash where you live, just take the stuff and throw it in the trash. If you cannot throw it away, I agree with the others that you should just leave it on the floor or the porch after stating that you already said you don't need the junk. It also sounds to me like she has some sort of OCD, and there's not a whole lot you can do to help it. But you do not
have to participate in it by taking the junk.
I feel your irritation. . . my grandmother is the same way. Our conversations also consist of her describing various junk and asking if we want it. Now, it's gone a step further. She asks every visitor and caller if they want the junk since the family didn't want it. Then, she calls my dad (her only child) and tells him to deliver said junk to so-and-so. And harps on it until we can't stand it anymore and deliver the stupid rooster lamp to so-and-so, who only said she'd take it becasue she was trying to be polite to a nice 88 yr. old woman.
I cannot stand clutter in any form at all. There is not one item in my house that doesn't have a useful purpose, except for the exactly 10 items in the curio cabinet for decoration. Gmas house makes me want to rent a dumpster every time I visit!! For example, she has a huge suitcase full of broken earrings, fuses, just miscellaneous junk. In the suitcase, we found my great-grandfather's BIRTH CERTIFICATE that he had reissued in 1946.
Another option -- At our work, we have a gag White Elephant gift exchange. I take some of the most awful stuff to that and give it away in a big box. My White Elephant gifts are the best!!