You might want to bring her in for a special feeding, of that cat food she loved so much, each morning and night for a couple of days till she regains full health and stamina. Sounds like she was just malnourished. Try to verify she is eating while in coop. Plus make sure all chicks get a well balanced diet that includes veggies, fruits and meat protein (dry cat food). I don't believe they get enough nutrition from dry commercial feed alone. I know I've bought several different kinds and each one has different ingredients and percentages and none had any real meal protein. Mine free range in the woods so they get lots of bugs but I also buy crickets once a month and feed them shredded cheese, dry cat food, and black oil sunflower seeds daily.