A chicken respiratory infection is like when you get a cold. Their sinuses can swell and cause eyes to water, and sometimes there's facial swelling. Like our colds, it often gets better on its own.
However, there are serious respiratory infections and one can cause sores inside the mouth, and these sores can be painful and make it difficult for a chicken to eat and to swallow. This kind of respiratory infection needs to be treated with an oral antibiotic such as Tylosin.
As @Wyorp Rock mentioned, you should look inside the hen's mouth to see if there are these sores. If you see these sores, then you will know that the hen is seriously sick and needs an antibiotic.
Could be, but if there's crop issues, possibly thrush?
I still don't have a clear idea of symptoms, but if the eye is swollen and there is respiratory symptoms too - possibly the cause would be respiratory disease. Quite a few possibles here.