One of my hens (approx 6 months old) decided she didn't want to come of of the box one morning. That evening she was in the same place, not having left the box at all. I tried to feed and water her, but she wasn't interested. We left food and water where she could reach it, but to my knowledge she didn't have any. After over 48 hours of this I took her out of the nesting box and tried to get her to eat yogurt and applesauce, she wouldn't even open her mouth. I inspected her but could find nothing obvious wrong with her. When I walked away she slowly walked back to the box and sat back down in it with her feathers all puffed up. I tried moving the nesting box to the porch, hoping avoid contaminating the other chickens should she be sick. After six days I decided t cull her. I dug a hole, and got the necessary tools together. I carried the box to the side of the hole and took her out. After six days of not eating she still had the strength to fight me. I decided to try feeding her once more and this time she ate, even mustering the energy to scratch around the yard for a while. That was three weeks ago. Since then she still won't leave the box voluntarily, but if I force her out she will eat and drink with the others for an hour or so, then return to the coop/nesting box and stay there indefinitely, puffed up, until I make her get out again. She is very thin and I'm still a bit worried about her getting the other chickens sick if there is something wrong with her. Any advice would be appreciated.