Today's update - she seemed very weak this morning - perhaps bc it had been so long since she'd had water - I don't know.
Poop is bright green, and obviously, she hasn't been eating any greens in days. I know it can just be sign of starvation - she likely didn't get enough food on Friday, and perhaps meals were too spread out yesterday, but I'm also seeing it come up as a sign of Marek's

Can it also signify just failing digestive system? To my knowledge, all of the chicks and adults have been vaccinated against Marek's, but I know that just decreases the risk and doesn't fully eliminate it. I don't have a place to fully isolate her, and at this point, if she has something contagious, I'm sure everyone has been exposed, so she is separated for her safety, but not quarantined.
Before all this, her vent feathers were already to the point where I knew I needed to find time to clip them and clean her up, but now they're badly caked with poop, so I'll figure out a time to tackle that today. I didn't want to do it right after feeding her to give her time to rest and digest.
When I placed her back in her crate, I had to position her so that her beak didn't fill with wood chips and the eye that seems to work better could see. At one point, it looked like maybe we'd given her too much water - she had clear fluid/bubbles leaking out of her mouth; it seemed to stop once I propped her head a little more upright with something under her neck, so I don't know if this was just positional and/or points to rapid decline.
I didn't find tube feeding supplies locally, but I'm going to order some - it seems like they'll be useful to have on hand no matter what. And, I've found a vet that sees chickens, but they're not open on Sundays, so assuming she makes it until tomorrow, I think I'll likely take her in - if nothing else, get a professional opinion on whether she has a chance of recovery, or whether euthanasia would be most humane.