Hi Gary,
If you can figure out which one is doing the pecking you should separate her from the others. If there are wounds you should buy a product called Blu-Kote to cover the bare areas so that the sight of blood and pink flesh does not encourage cannibalism. If they begin to draw blood, you may find it impossible to keep them from eating one another.
Some people have reported good results with a patch of duct tape across the affected area, but that's usually for pecking on the back.
Others have suggested "peepers" which are anti-peck devices.
I have no experience with this, but I have read threads with the following suggestions:
1) increase protein (black oil sunflowers, fish, game bird feed) because sometimes pecking is a protein deficiency.
2) make sure the chickens are busy and occupied all day so that they don't have time to peck. Free range them, or hang a cabbage from a string in the coop just out of their standing range so they have to jump up, etc. Boredom causes pecking.
3. Get rid of or eat the offender and hope that the others have not learned the bad behavior.
Good luck, and you can try a search on feather picking, cannibalism, and peepers to get more info.
Renee