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