I am not an expert.
I know it looks horrible but I’ve seen amazing feats of healing take place with people’s chickens here on BYC.
Bring the bird inside and get it cleaned up gently but thoroughly with soap and water. Pat dry.
Coat the entire wound with antibiotic ointment -NOT the kind that has a pain reliever in it.
Hopefully someone else will make a suggestion about bandaging or not to bandage.
Prepare a quiet, dark, safe place for the bird to recuperate in tonight.
Replacing electrolytes might me a good idea but at the very least see if she’ll drink some water. and provide food although she may not eat tonight because of the shock she’s experienced.
You’ll want to keep her inside during recovery to minimize the risk of infection and re-injury from flockmates.
A dog crate is ideal but you can improvise. Even a box or clothesbasket will do for tonight.
Also some people swear by Manuka honey for wound healing.
I hope some of this helps and she heals quickly.