Sick Chook

Had a light Sussex on Baytril ( per the vet for 10 Days) Was on Metacam as well for the first 7 days.   She had improved until last Friday and thought she was on the mend.  Now she has stopped moving around- her legs are stiff .  SHe had no swellings. Her comb is now quite pink .  Has a mucky back end.  Is wating scrambled egg and sausage peas & sweetcorn. A little bit of Pellets but how much is difficult to actually see. She has lost half her weight I suspect by the feels of her.  Vet has suggsted keeping her on the Baytril , but I really thingk it's more the stiff leff thing...Any siggstion of what it might be as can find nothing on the internet with similar symptoms