Hi, sorry this happened. Start by making up a batch of sterile saline solution. Boil some water, let it cool, put one cup in a clean jar or other vessel. Add ½ teaspoon of non-iodized salt and a pinch of baking soda. Shake or stir to dissolve. I like to put it in a clean spray bottle and spray the wound thoroughly, that way I'm not scrubbing an already sore area. You may also want to purchase a product like Hibiclens spray at your feed store.
Next, gently blot dry with a clean towel. Maybe clip feathers away around the wound so you can see better and feathers don't stick in the wound.
Finally, dab the wound with triple antibiotic ointment that does NOT contain pain reliever. Like Neosporin Original or its generic equivalent. Do not bandage. Can you put her in a dog crate so other chickens cannot peck her but she can see and be near them? Repeat the wash, blot, ointment twice a day. Give her regular feed and grit. If she won't eat, try adding water to make a thin gruel.
Let us know how she does and good luck. Welcome to BYC! Wish it was under better circumstances!