You need to bring her inside (away from flies) and clean her wounds. She will probably struggle against you, but it is really important that you are able to be thorough and to really see all, exactly what has happened. It is also a good idea to cut back any feathers that might be trying to touch the wounds. You need to ascertain whether any bones have been broken and just how bad the wounds really are.
I'm very sorry. I have dealt with raccoon problems before. I'm sorry to welcome you under such difficult circumstances, but welcome to BYC.
Once you catch her you need to decide whether her wounds are treatable. Chickens can heal from pretty nasty injuries usually, so keep that in mind. Trim back her feathers ans clean the wounds with peroxide or (I prefer) betadine tea (1 part betadine to 10 parts water). Really clean the area well. I use a turkey baster and a soft brush to get the wound clean and remove any ground in debris. After cleaning a wound dressing needs to be applied. Neosporin (without any pain reliever) works well. Blukote also works, but burns going on. I wouldn't try to cover the wounds with bandages. Keep the bird inside where she can be warm and dry. Feed her some tempting snacks- scrambled eggs, plain yogurt, sunflower seeds. Maybe give some electrolytes in the water for shock.
Keep the wound dressed to keep it moist and infection free. Clean it as needed with the betadine tea or plain old saline (weak salt water). Don't use peroxide after the first cleaning unless you see signs of infection. Watch for signs of infection- redness, odor, swelling, sudden increase in oozing. Some would start her on antibiotics immediately because of the nasty nature of raccoon bites, but I prefer to wait until I actually see an infection before I treat for one.
Keep her out of her coopmates' reach until she heals up.