Just wait for the Tiagard as that may help her. I suspect that rooster minimally had a URI (upper respiratory infection) or MG (Mycoplasma gallisepticum). I'd have her separated where she's kept warm and try to push fluids. You can make a mash out of her crumbles/pellets and water, or try scrambled eggs to keep her eating.
I'd also get some chicken vitamins and get them all on some. Poultry Cell and Nutri-Drench are for their water. Vitamins gives them a boost to fight off infections.
When the Tiagard gets there, I know you said your other chickens got over it, but check carefully and also give it to whoever else is still experiencing symptoms at that point.