Plucked Chicken in the Cold? Help!

[Spark]

A few weeks ago some of our chickens plucked the feathers on our australorp's back. There's a good sized bare spot near the base of her tail now, and today's temperature dropped to 22 degrees. When I let them out this morning I noticed the bare spot looked red and irritated. I'm not sure whether or not the rest of the flock was aggravating it again (from what I saw nobody was picking on her) or if it’s from the cold, but I’m guessing the latter. I know people say to put petroleum jelly on their chickens combs in the winter for frostbite, but could we do the same thing for her back? Would the other chickens be more (or less) likely to peck at it if we did?