Does the wound smell bad, have pus or other discharge, or have maggots? It's hard to tell from the photo, is the crust mostly dried scab, or is it wet and full of dirt?
Chickens are very resilient to external wounds as long as there isn't too much internal damage and infection doesn't set in. If she were mine, I would first clean her up the best I could with chlorhexidine and water to get a better idea of what you're dealing with. If it's not a big deep infected wound, I would give her a chance by drying her well, and setting her up in a "chicken ICU" in a clean warm place with water w/ electrolytes, whatever food might tempt her to eat like scrambled eggs or feed mixed with water.
Let us know how she does!