ckicken trouble

Hello and welcome to the forum.   

Could your hen be broody?  If she is broody she will fluff up her feathers and growl at you if you try to move her and be generally rather cranky.  Broody hens will not eat or drink apart from once a day when they go out and do an enormous pooh and eat/drink a little.  You have to take them off the nest once a day to make sure they have something to eat and drink as they have been known to starve themselves.

When you say she has just been sick do you mean that she has been generally under the weather or she has just regurgitated?

A little more info would help us to help you. 
Does she have a temperature?  You can tell this if you feel under the wing of one of your other birds then under hers to see if she feels warmer.
How does her crop feel?
How is her breathing? Is she gasping, rattley or does she have a runny nose?
How are her eyes? Clear or weepy?
What colour is her comb?
Is she poohing at all?
Have you checked for lice mites and worms or other little visitors?
Does she have an egg stuck in her vent?
Do you know what age and breed she is?

Sorry to pelt you with all these questions    Good luck with your hen and keep us posted