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When was she treated by the Vet and what did the vet give her (medication/dosing)?
Did the vet perform a fecal float?
It looks to me like she is still suffering from respiratory disease. Did the vet "name" the disease? Infectious Bronchitis, Mycoplasma and ILT are a few of the more common diseases chickens can have.
How old is she? Does she lay eggs? Have you noticed if she has any fluid or swelling in the abdomen? How does her crop feel? What does her poop look like?
If it's possible, contact your vet again and tell them she is declining. Depending on what she was treated with, she may need a different antibiotic/treatment.
It would be worth looking inside her beak to make sure there are no lesions, plaques or evidence of Canker too (white/yellow cheesy patches).