Although, the postmortem findings with aspergillosis is supposed to be "Grayish yellow lungs" according to one of the chicken health books I have.
I went through all the diseases in that book, and came up with two possibilities based on the symptoms and postmortem findings. One was Botulism and the other was Toxoplasmosis. Both cause paralysis (with botulism, it's limp paralysis, which was one of Margo's symptoms...limpness. But Toxoplasmosis was the only one that had the postmortem findings of "Blood-filled Lungs" (ie, red-tinged). I'm a newb, and I'm just going by the books I've studied, but I wonder if either Botulism or Toxoplasmosis could be a possibility. Especially since there are so many stray cats all over the world that spread Toxoplasmosis. Insects eat the infected cat poop, get the protozoa parasite, the chickens eat the insect, and boom, they have it too. Supposedly both diseases are "rare", but they're still a possibility.