Better pictures once cleaned up might help, of the wound and so we can tell exactly where it is.
Does this bird roost normally, or lay in bedding somewhere? If she's not feeling well, she's likely to be picked on. If she's not roosting normally this could be a breast blister. Cannibalism (birds will peck anything red or bleeding) is possible.
I would clean it up well, and apply plain neosporin or plain triple antibiotic ointment a couple of times a day to keep it covered. I would also keep her on clean towels or puppy pads rather than any loose type bedding, to help keep it clean. And keep her separated from the others until it's healed enough to not be a pecking risk.
Give her a good going over to check for general health and body condition. Is she thin or good weight? Check bottoms of feet for signs of bumblefoot.