Vent gleet and molting? Not sure

[Fallenoak]

Hi! I have chickens that are just over a year old. Hen in question is a sex link. Forgive me if I’ve gone about this all wrong, I’m a new chicken owner and this is our first health issue. We had a bad bad cold and snow spell back in January and I was really worried about the birds but they did fine. Shortly after that, I cannot remember the exact date, sometime in Feb, one of the gals started losing her feathers. I thought it was just a bad molt. It started at her head/neck area and then moved to the bottom. I can see some pin feathers growing back all over. Her bottom is nearly bare now, and just in the last week or so I noticed a very poopy bottom. I didn’t think much of it, thought it was just due to the bare butt. I have noticed some separation from the flock for awhile, but thought she was just tired from growing new feathers? No bullying or anything. Today she has been acting very sick suddenly. Moving very slow, breathing hard, sitting hunched, falling asleep. I started doing some research and gave her a bath and got her bottom as clean as I could. Her vent looks swollen. Idk what the crop should feel like but it’s not swollen. She is definitely smaller than the rest of the flock. I think she’s been losing weight. I thought it was just the loss of feathers making her look smaller, but now I definitely think she’s smaller. Her poop seems to be diarrhea. She is eating and foraging some, but very very low energy. The rest of the flock is totally fine. What can I do? I cannot take her to the vet.