Can you give a few more details, such as how old, how long you have had her, and if any birds have recently been added to your flock? Does she seem weak from the heat or dehydrated? Give her some water with SaveAChick or other brand of electrolytes. It kind of sounds like she could be having signs of a respiratory disease with the nasal drainage and head shaking. Sneezing, gasping, or rattly breathing can be other signs. If you think it may be respiratory, antibiotics such as Tylan or oxytetracycline can be used for treatment, but they won't help if it is fungal or a virus.