Previous posts have covered many of the things below:
Peace, quiet, warmth, time.
I had a roo 13 years ago that was in such bad shape from an attack and was nearly frozen to death when I found him (he pretty much showed up out of nowhere). He couldn't move, eat or drink for 7 days. I had him in a crate/box in a quiet warm room with soft music for that week.
He made a complete recovery. Finally stood after a week and decided he was in it for the long haul. A week or two later he was crowing to beat the band. And this was before I knew how to treat him - every place I called was beyond clueless also. At that time, all the feed stores I called said roo food was scratch and nothing else so he wasn't even getting good nutrition.
Oral antibiotics for the bacteria conveyed by the cat - wildlife rescue centers know the right kind to use because they are constantly dealing with cat attacks. Although a chicken is a great deal larger than usual cat prey (mice, little birds), this antibiotic may be crucial to her survival.
Topical antibiotic on the wounds.
As Spotted suggested, aspirin may help with the pain and give her some comfort during this most difficult time. Assuming she's not bleeding badly. 5 regular (325 mg) pure aspirin (NO SUBSTITUTES) crushed per gallon of water is the usual dose recommended on BYC. If she's not drinking on her own, you may have to very very slowly dribble a little from an eyedropper along her beak and let her swallow on her own.
I wouldn't worry about food just yet, till she's had a chance to calm down, be less in shock etc.
Hoping very much that she'll be alright.
JJ
