Many respiratory infections are eye-shut and nasal discharge. It could be infectious Coryza (smell her beak, if its fetid it could be coryza), it could just be a cold.
I just dealt with this and when they get lethargic, they don't drink enough. I suggest you use a syringe (without a needle) and go out a few times per day and squirt some of their antibiotic water into her mouth. This helps you ensure they have medicine. Also feed them some yogurt so they can get some nutrition. I have had a few birds die from things like this and it was because I couldn't keep them hydrated (tough lesson), and I have pulled 6 thru it because I nursed them with liquids and food.
Watch your other birds, isolate her if you can. If she gets bad, go for the Tylan 50.