Quote: What type of food/treats do you feed? What is her normal feed?
You mention that she may be suffering from malnutrition? I recommend that you give her a balanced poultry feed (chick starter, flock raiser or layer feed), oyster shell free choice and poultry vitamins like Poultry Nutri-Drench or Rooster Booster Poultry Cell. Hard boiled/scrambled eggs or tuna for extra protein and little amount of some fresh greens/veggies would be good.
If she has been picked, the other may be keeping her from food as well. This could be the cause of her decline. Nutrition and watching to see if she is drinking well will be helpful. Her limping can be from a number of things - sprains and injury are common. By keeping her separated, hopefully with some rest the limping will improve. Sprains can take several days to start to heal depending on how severe they are.
Keep us posted.