Hen with missing back feathers

[Tiggerteri]

I have a hen who has lost all her back feathers due to an aggressive rooster. The rooster is gone now but her feathers are not coming back!! This has been almost 4 months ago. This happened to one of my other hens but her feathers came back. Any suggestions?? We’re just starting summer so I want to figure this out before winter comes

 

[Cyprus]

Try feather fixer feed. I was once in the same situation.