Just thought I'd pop back on here with another update. After a few days where things seemed touch-and-go, I think Red has turned the corner. For a couple of days, she really just wouldn't eat, and was going to bed with an empty crop. I was finally able to bribe her to eat with tomatoes and hot dog buns soaked in electrolyte water & probiotics- she became VERY enthusiastic about eating both of those things, which then led to her eating pellets again. Today was the first day that she was back to her bossy, hungry self. She was walking around like a normal chicken, eating all that she could find and insisting everyone else treat her like the head hen that she is. I'm so relieved- all of my girls are pets, but Red is special.
My Golden Comet is now about 2 days into acting exactly like Red was. Poking around at food but barely eating, slimy milky poop, hunched up looking uncomfortable, but then running off when you approach her like nothing's wrong. I'm obviously watching her very closely, but since this is almost exactly the same as what Red just went through, I'll just continue to try to interest her in whatever food she'll eat and hope she rides it out in a week or so.
A few of the others are also having slightly slimy poop, though none of the rest are off their food or looking so miserable.
The whole group will get their second round of dewormer next weekend. I haven't seen any worms/eggs expelled, so not sure what's going inside their little digestive systems, but something's clearly running through them. The next week is supposed to be a lot warmer, generally up above freezing, so I'm hoping that will help too.