It seems like she has some distress when breathing for sure, but its difficult to know exactly what might be the cause - it could be bacterial, viral, fungal, allergic reaction. Do any of your other chickens have the same symptoms? If you do have others, then i would suggest isolating this one, but to be honest its more than likely that the rest of your flock has caught whatever it is.
In your situation, i would give vitamin / electrolytes in her drinking water and administer a broad spectrum antibiotic. I must point out that many members here would not give antibiotics without knowing precisely what the problem is. I do not follow that line of thinking, as veterinary care grossly outweighs the cost of a bird and i am not prepared to do that.
Hope this helps a little