Welcome to the world of chickens! Sometimes it's really hard to tell what's going on with them if there's no physical symptoms that make it obvious (hard or squishy crop, etc). Whenever I have a hen that seems a bit off or troubled, I always put them in the "hospital box" we built in the garage, which has food/water, heat lamp, clean shavings, etc. I also put an electrolyte in the water (try chick saver brand) or even just plain apple cider vinegar. My 50+ hens all free range, and just recently some of them got into some mushrooms which I've since discovered are poisonous - could that be it for yours? I live in the pacific NW, and apparently it's been a banner year for this particular type of mushroom because it's been all over the news. I went through our acreage and tried to remove them all. You might want to check also to make sure they're not eating long peices of grass, and make sure they access to grit at all times. Do your hens free range? Sometimes, too, I've noticed that chickens from feed stores just don't seem to do as well as chickens I've bought locally or hatched here on the farm. If her poop is super watery, it sounds like maybe she has diarrhea, so an electrolyte will definitely help. Personally, I don't like to load up a sick chicken with a bunch of medication (delouser, dewormer, etc) unless I'm positive what the problem is..... Anyway, I would isolate her in a safe warm place and see how she does. It sounds to me like maybe she got into something that's disagreeing with her.