I'm not an expert on matters of chicken health. I'm just hoping to bring you back to the top of the list so someone else will see your thread.
Thank heavens you have her separated! Respiratory ailments are very bad. Make sure you tend to your other birds first, so you don't carry any germs to them.
She needs antibiotics. This assumes that her ailment is bacterial, and it may not be bacterial. I like Sulmet. Probably because I own Sulmet, and it is cheap, easy to find, and easy to administer. There are lots of other opinions out there, and they belong to people who know more about it than I do. These more knowledgeable people will need more details from you. Things like: Do you notice any swelling of her face or wattles? Is there any mucous around her nostrils? Is she sneezing? Is there any sort of bad smell around her head? Is she eating, drinking, acting normally? That sort of thing.
Good luck to you.
Edited to add: Just noticed you are in NZ. I have no idea what medications are available to you there.
