This is where I really like to use Hemp Protien Powder. It will not only nourish the hen, but stimulate her appetite. Have you tried giving her some chopped pieces of cooked meat? Chickens are wired to crave protein when they are weak. It gives a physical boost to endure harsh environments. Also, high energy fruit like black or red grapes, diced up. Creamed corn is also enticing, put a little in her mouth with a spoon or straw, to get her going. She'll need some serious pampering to get her back on her feet.
If she is drinking, that is good, you can add some aloe vera with a bit of apple juice to heal her digestive system and provide energy too. Sugar water is good but has no nutrients, give her some Nutri Drench to provide vitamins. .
Yes, that runny watery poop is the water going through her digestive system with not enough food to create bulk.
If you can syringe feed by grinding some feed in a spice mill or blender, then sifting it so that it doesn't plug the syringe. If it does, cut the tip of the syringe to make a bigger outlet for the food. Add some water to the sifted feed to make a slurry. Then, suck it up into the syringe and feed that little girl.
Sometimes you gotta think outside of the box, you got this!
God Bless!