I'd wash the wound with soap and water and rinse it well.
Apply pressure to get the bleeding to stop. If it won't apply styptic powder. Then dab the area with Vetericyn or equivalent antiseptic treatment.
You may want to cover it with a bit of pine tar to protect it from flies and the other chickens. I would inspect it twice a day and add more pine tar as needed. She will look a mess because of the tar until it scabs over but it will heal just fine as long as you keep it disinfected and free of flies.