Poor girl.
I hope you can get a vet to see her today. It's Saturday - you'll have better luck than tryingto see avet on a Sunday.
Many things are quite fixable if treated in time and turn out poorly or worse if not.
Hoping for her....she needs relief from feeling so sick.....
During regular working hours; go to the NC state Vet School web site. Then call the number given for the poultry or small animal school. The Doctor/Professor there will talk with you.
If it (hopefully not) comes to the point where you think this hen will need to be put down - then the school will euthanize it for free and give you an amazingly long report on your hen. This is especially good if you are concerned about the hen having a contagious disease that could wipe out your flock.
I currently have a hen with a purple comb as well she is standing around all puffed up. However unlike your hen she is not throwing up, and she is eating and drinking normally. I have her separated at the moment and she is on medication. My suggestion is to separate because it could be contagious. Whenever a bird is sick you should always separate no matter what. As for the throwing up, quiet often chickens will throw up when they are either overly stressed or Scared. so she may be REALLY stressed and that may be what is causing it.... I assume its a sickness though