I would repost under Emergencies but till then...
How old? Is she laying? Are there any signs of frostbite? Discolored comb, feet, toes from pale, yellow, purple, black coloring. Is her breathing normal? Any wheezing, raspy, gurgling noises when she breathes? Is her crop soft, mushy feeling or hard lumpy? Is the crop empty in morning and does she fill it up at night? Any strong foul odor coming from head or hinney? Any injuries, signs of lice/mite infestation around vent or under wings? Any sign of worms in poo? Any mucus around eyes, nasal, any bubbles around the eyes?
I would inspect her crop as vomiting is from crop and may be sour or blocked. I would get a tube feeding kit to get her hydrated and get liquified food into her. Kaytee baby bird food is good for tube feeding. Gently massage the crop to get things moving. Yogurt, and womens vaginal yeast meds can be used for sour crop, to break up a blocking mass water and massage.
Id also take a pic of chicken, poo, and vomit and post in the Emergencies thread. Very awesome people to give you advice and possible treatments. I myself am still a rookie.