how old is the hen?
please describe the droppings..color and consistency
has she been wormed? if so when? and what was used?
has she been laying eggs?
please check crop for possible impaction..
also check mouth and throat for whitish or yellowish plaque or sores, and any odor.
if you find any lump in the crop, or sores in mouth or throat..
post back and describe.
could she have got into anything that went moldy or bad..(kitchen scraps/spilled feed/dead rodent, etc..)
any access to car oils/chemicals, fertilizers/weed killer/any other toxins?
separate her to a warm safe place.
in her weakened state she is not able to really compete for food and water.
please make up a mix of a little oatmeal cooked with water, layer feed, chopped cooked egg yolk, and plain active culture yogurt.
hand feed if necessary, by rolling mix into pellets, placing in mouth and stroking throat downwards to encourage swallowing.
also have regular feed available.
put vitamins in water and if she is unable to drink..give by drops on beak,,don't pour down the throat.
this could be nutritional..a deficiency of some kind.
wouldn't hurt to check her feet for any sores or scabs..
check legs, back, and hip areas for any possible injury..
check eyes for anything odd, cloudy, or gray.