What does her poop look like? It can tell you a lot about her condition. How old is she?
I can see that she's sick, though. There are so many chicken diseases, it's impossible to say what it could be that's making your hen sick.
If it's viral, antibiotics won't help, but on the off chance she has an infection of some sort, why not start her on an antibiotic? If it's going to help, you should see improvement in 24 hours.
Her head movement may indicate discomfort in her crop. Do you feel anything hard in it?
Has she been laying? How long since she laid an egg?
Sorry, this is the best I can do with the information you've provided. You might follow the sticky up top and answer all the questions. It would give us more to go on.