As always, with chickens, it could be lots of things.
When chickens molt it takes a lot of energy to regrow feathers.
If she's not eating enough, she's going to have trouble warming herself.
She definitely needs to be kept in a warm place until you figure out whats going on and hopefully get her better.
80-85 degrees is optimal.
Does her crop feel normal? Does it empty after she eats? Is she drinking well?
You said she was injured by a rooster. How long ago, and what was the injury? Is she completely recovered?
If the feather loss is mostly on her back you can try a hen saddle. That will also help keep her warm if her back is just bare.
If it's not the crop then I can only tell you what I'd do if it was me. DE is really not effective inside a chicken.
If you have a vet that will do a fecal float test for you that would verify or eliminate worms as an issue.
If that isn't an option I would go ahead and worm with Safeguard or Valbazen (albendazole, fenbendazole).
A worm infestation can cause a molt or contribute to a heavy one. Often you will see runny poos, but not always.
And not necessarily visible worms. Would account for weight loss and not eating well too.
That's just where I would start, since it's common and simple.
You may need to look at hand, syringe, or tube feeding if she isn't getting enough.
Casportpony has some really good posts on that and how much they need every day.
Do a search at the top of the forum for Tube feeding, it'll come up.
Best of luck, perhaps someone else will have other ideas.
