Separate her. Soak her in a deep tub of lukewarm water and a little Hydrogen Peroxide. Probably will have to soak at least an hour ... and the scab will not come off at this point .... then spray with vetricyn and apply Neosporin antibiotic cream. Spray with vetericyn 3x daily and keep applying neosporin. Hopefully, as the neosporin absorbs into the skin the old scab will come off and you can see what the wound looks like. Hopefully no fly-strike or anything like that is present. Keep the wound moist with neosporin and hopefully she will start to heal from the inside out.
This is how I treated my hen that had wounds due to roosters spurs ... so it is not the same as yours, or in the same place, but it is still what I would do. Also, I am no expert at treating chicken wounds.
A vet would be advised.