How is her behavior? The poop looks like a reproductive infection is flaring up.
That's my suspicion too. And I should clarify - that's why I mentioned necropsy in an earlier post; the 2nd time i brought Masha in, this summer, the vet offered me information on a poultry necropsy that the dept of ag (I think) could do when the time comes for her, to make sure she didn't have something especially bad and contagious (which he didn't necessarily expect) and, in the process, it would reveal the extent of her reproductive disease. The reasons for her 1st and 2nd visit were a lash egg most likely laid by her (& her egg laying had plummeted to maybe 2x/month over the previous several months, with some thin & soft- shelled ones more recently); diagnosis of what had developed into a large-size hernia at her lower abdomen (which I had assumed was a tumor based on the egg-laying issue), & decreased mobility (hardly ever leaving the run anymore, difficulty jumping down from roost bars).
The temps for several days before this polar vortex were in the 60s & 70s. And guess what? Masha was outside in the chicken yard walking around, dust bathing out there again (versus only dust bathing in the run). She still couldn't venture out of that yard with the others to forage, but daily excursions outside and more enthusiasm was awesome to see. Then suddenly, stuck inside for days, heavy rain, then frozen rain, then snow, for days, with those strong N winds we get. All the others did fine in the wrapped run, temps inside getting down into the single digits. Related? Maybe, maybe not.
I also just had to treat the flock 1 week ago for Roundworms (with Valbazen; re-dosing next week).
Behaviorally: on the positive side, a couple hours ago she showed the first interest in food since I brought her in Thurs night, and even ate some mash out of a bowl herself (but then she shook her head after almost every bite and flung some around the room. Woah.). (And no leaking liquid while she did.)
Negative: today she hasn't tried to walk around the room at all. Just standing there with her head down. She must be weak for lack of real eating and drinking, but she surely must be in some real discomfort.
Previously she'd wanted to take steps to where I've been doing my office work and also sit on my lap and just hang around. She may be getting depressed too.
Stool: Nothing from her back end since very late last night, and that was 99% liquid.