Lethargic, puffy, eyes closed, clear watery poop - going on 6 weeks now

I have a hen that's been ailing for about 6 weeks. Treated with fenbendazole originally and she seemed to perk up. After that she improved steadily, little by little for 3-4 weeks. Then the last two days she's downhill again.

Today she just stood in the corner of the coop, puffed and eyes closed, occasionally shaking her head. I picked her up and felt her crop and it seemed empty except for crispy things - I assume their granite grit. Then I saw her poop and it was nearly clear, with a tiny bit of pale yellow/white. Now I've got her inside a dog crate in the garage. She pooped in the crate again and it was so clear I couldn't even see it on the shavings, though it smelled very strong and sour. I did weigh her and she hasn't changed weight since this started a month and a half ago.

I'm just not sure what's going on, or why she's just generally ill and not making a real recovery. I feel like it can't be worms since we just treated for that. I do have some durvet duramycin on hand - should I give that a try? I have Corid as well, but they all had a run with coccidia as chicks and made full recoveries. She also has not laid an egg in weeks, as far as I know.

At a loss, and afraid she's got cancer or something and will linger before dying. Ugh. All the other chickens are doing great and laying extremely well. Why isn't she??

 

Ours ultimately seemed to have a bowel impaction. She eventually produced a very hard, somewhat dry poop consisting mostly of hay, which had been shredded into fine hair-like fibers that were densely packed. Now that she has passed this, she's much more energetic and eating and drinking well. She still shows no sign of laying, but is pooping normally. She did give herself an anal fissure in the process, which we are keeping an eye on. For the moment she's isolated in the garage to heal.

The plan now is to remove all hay from the coop. There was not much to begin with, but we had a bit in the nest boxes as it kept the eggs cleaner than shavings, and some hay in the run to combat moisture from snow melt. None of the other hens have had any problems with the hay. So I do still wonder if she has a bowel issue the others don't, and whether she will ever produce or be normal. Time will tell on that one.