sick chicken

This poor bird is big and ugly. When we got her, the rooster had pulled all her back feathers out. She got a reprieve from the rooster, started growing new feathers, and then our dog got a hold of her. She had a bad puncture wound in her back that healed very well with a pine tar/iodine remedy that a friend showed me.

She is the dominant bird in the flock. I started isolating her because she leads the flock in picking on the small, skittish hen. Now she has developed a red patch on her wing that lost feathers. It has been irritated for several months now. More recently, she is losing more feathers, not producing eggs, and has diarrhea. Otherwise, she is still the dominant bird in the flock when she's with them; she's quite strong, energetic, and cocky.

I'm wondering what to do about the red patch on her wing, and what can I give her to help boost her immune system and grow some more eggs?