From the yellowish tint in part of her poop, her general apathy, and the fact that she slept in a nesting box, I would suggest that she is egg-bound, or that she has a broken egg inside of her. Either one of these things could be life-threatening, and I have treated two or three of my hens that were afflicted by this, so I think I can be of some help.
First, look at her vent to see if there is anything sticking out. If there is reddish tissue sticking out, this is probably her oviduct and you do NOT want to try to remove it. Instead, gently push the tissue back into her vent, and gently squirt cold water into her vent (the cold water shocks the muscles and encourages them to contract and keep the oviduct inside her body). You may have to do this a few times for a few days before her muscles actually start keeping the oviduct contracted.
If there is no reddish tissue, check to see if there is anything whitish, yellowish, or brownish hanging out of the vent. If it is somewhat rubbery, this is probably softened egg shell resulting, most likely, from malformations of the egg and/or broken shell. Gently and slowly pull this tissue out (as much as you can). Most of it (if not all) should come out with some gentle pulling, but if only a part of it will come out and the rest is stuck, cut the removed part away from the stubborn part.
Next, make sure your chicken has a soft-foods diet, like yogurt and scrambled eggs. Eggbound hens often cannot pass feces very well, and as the issue progresses it becomes impossible for them to pass feces and they eventually die from the toxins accumulated in their bodies. Soft foods will be easier for the hen to pass. Also make sure she has plenty of clean, cool water with water-soluble vitamins in it.
Now you will want to give your hen a bath. It sounds silly, but it really does help. Fill your tub, sink, or dishpan with warm (or even very warm) water up to a little above the hen's crop-height. Gently place your hen in the water until her abdomen and vent are completely submerged. If she freaks out, you will have to hold her down, but in my experience, hens placed into the water slowly and gently will actually like it and will need little to no restraint. Begin massaging her abdomen, from the front to the back near the vent, for several minutes. (Often, this encourages her to poop, so be prepared for a mess in the water.) After about ten minutes of soaking and massaging, remove her from the water, gently dry her, and separate her from the rest of the flock. Often it is advisable to keep her indoors in the presence of extra heat (but not so much that she begins to pant). Continue her soft-foods diet and give her one or two baths a day.
If after this she shows no improvement, I would take her to a vet. A vet does not have to be an avian vet to treat chickens. My local animal hospital treats all sorts of animals, from exotic pets to farm animals. I would call around and ask local vets if they can treat chickens. Not all vets will, of course, but some of them may surprise you.
I hope this has been helpful. Be sure to look around this part of BYC for other tips on egg-bound hens. Typing in "egg-bound" in the search bar should bring up some really helpful tips from past flock owners who have dealt with this issue.
God bless,
~Gresh~
I would like to find a good chicken vet.
