EMERGENCY!! Sick hen in the nesting box

Get a heat lamp set up, or get her next to to a fire. I myself had a case of chicken hypothermia just tonight, but it was solved. I stuck her under a heat lamp and she was fine, I hope your situation goes as well, make sure she has food and water in front of her

 

Start checking her for being egg bound,crop issues,vent gleet,mites/lice/worms.

To check for egg binding,put on gloves w lubricant and insert finger into vent,see if you can feel an egg or broken egg shell. If yes,give her a calcium or tums tablet or liquid calcium,keep her somewhere dark keep her warm and relaxed. Normally you could also give her a warm water soak,but in her condition it is not recommended.

To check for impacted crop,check her crop at night(after eating all day)should be full,check in morning(before eating)should be empty. For sour crop,crop may feel squishy and there might be a foul smell coming from mouth.

To check for mites/lice,look under wings,around base of tail feathers and around vent area. For worms,you probably will not see them,has she ever been wormed?

Vent gleet,does she have a whitish discharge from vent? Here is a link for vent gleet,just in case this is what you are seeing.

www.backyardchickens.com/a/vent-gleet-aka-nasty-chicken-butt

 

Second this.

The egg binding would be most severe and explain the behavior. Egg binding requires intervention or the chicken may perish.