Honking bird

Asking for advice about my 5 month old true blue whiting pullet. She has been making this noise for a month. She has been separated from the flock, and given Tiagard and vet RX. Aside from the noise, her behavior is completely normal. Her appetite seems normal. She is still a little too young to lay.

We just don’t know what to do. Is this a disease that could take out the whole flock?