Thanks for all the sympathy and advice, all. I just spoke with the vet. I am SO LUCKY to have found this vet! His staff had never seen a chicken before, he doesn't typically treat them, but he used to raise them himself and he really seems to know his stuff.
I was worrying about my other chickens, and specifically about Marek's. Goldilocks wasn't here long enough to really get attached to her, but oh, I would have been devastated if anything happened to LOVER BOY! Or even Crow, who came to me together with Goldie but has tons of personality, and she's just a few months old so would have been vulnerable to Marek's.
Doc says she did not appear to him to have had Marek's. He guesses old age. Her gizzard was very soft, and over-filled with stones. Liver looked OK although very small. Air sac showed sign of previous respiratory problem, but not so much an acute problem (like
flu).
Nothing reportable, nothing to worry about the others catching that a good scrubbing, Ivermectin and DE won't take care of. He had not heard about DE, by the way, was interested in it.
Off to do another load of laundry. Between my clothes, coats, and cushions, towels, etc. that she might have come into contact with, I've got about 10 loads to do
Then when the weather clears up as it's supposed to do this afternoon, I can SCRUB and move the Eglu to a fresh patch of grass.