Not always. Chickens can get exposed to MG or other diseases, and not show any symptoms. It can lie dormant in the body and one day show up if they are stressed. Denagard is said to have a bad taste, and sometimes chickens won’t drink enough. She can try flavoring the water, or mixing a small...
Her eye area looks very swollen, which can be from pus from a sinus infection. The pus needs to come out. Did your vet do a swab culture of her nasal or throat to test for MG? Does she have a bad odor from her face? If it is not MG, it could be coryza or another respiratory disease, or a...