Although as long as she is eating and drinking and the wound looks clean and not green and doesn't have pus in it, I would think she is likely not fighting infection.
I wouldn't wrap it if she isn't pecking at it too much. I used Pen-G injectable from Tractor Supply. I got syringes at my local pharmacy and they were much cheaper than at TS. I can't remember the dose, but if you find my thread on my girl who was attacked by a hawk, it has some links to dosing.
That is a lucky thing that you caught the fox in the act. I wouldn't worry too much about lost feathers. The wound being under her wing is probably a good thing. It will stay relatively clean under there and the others won't be as likely to peck at it.
Do you have a rooster? Could that be why...
Oh and if she will let you, I would at least run clean warm water over the injury. If you can put antibiotic ointment on, I would too. Make sure it does not have pain reliever in it though. If you can't get the ointment on her, I would get an wound spray to put on it. Where is the injury in...
I would think pedialyte would be ok. We have a packet of poultry electrolyte powder that we keep in our chicken first aid kit for this type of thing.
How did she get the injury?
I have had distressed chickens before and they usually breathe with beaks open when they are stressed. I would keep her quiet, give her water with electrolytes and a little soft food like scrambled egg or her feed with some water mixed in and let her hang out alone for the night and assess again...
She looks similar to my Brahma that is recuperating from a hawk attack. If you read the thread down a bit titled "Hawk attack, graphic pics", it has a ton of info on how we treated her. She is doing well after losing most of her shoulder and upper wing. It was huge and bloody and open and she...