We left for the three day weekend and had someone check our flock of 12 daily. Came home Monday afternoon to our SLW pullet struggling to stay upright and reaching her neck out to breathe. We immediately brought her in the house and checked her over. No obvious injury, no sneezing or wheezing, no mites, vent is clear, color remains great, crop feels fine, poo is normal. She wouldn't eat or drink on her own so I used a dropper to offer her some water and left her in the tub on a fleece "nest" not thinking she'd survive the night. When she did I called the vet who said to cull her. Sick chickens can't be helped and if she's suffering it's cruel to leave her as is. Instead I hit a farm supply store and picked up VetRx and electrolyte solution. I used a dropper to offer her some more infused water and softened her feed crumbles. I had to put it into her mouth for her but she happily swallowed and will perk up for a short time afterward. I applied the VetRx and have otherwise just let her rest. She survived last night and I did the same routine several times today also offering some scrambled egg. I expected her to either take a turn for the worse or show signs of improvement but her condition has stayed exactly the same. Gaped breathing with every breath, still won't eat or drink on her own, still incredibly unsteady on her feet. She's still very young at 9 weeks old. None of the others in the flock show any signs of illness and I'm struggling to sort out where she could have picked anything up. She lived the first 6-7 weeks inside in the brooder, the last 2 almost 3 outside in the coop not having spent anytime in the grass yet as I was waiting for them to get older. I'm completely new to having chickens and don't know what else to do for her. I tried the throat swab to check for gape worms but nothing. I also tried the controversial water/oil fill and empty of her crop and that produced no answers or relief either. I've researched online relentlessly and can't figure this out. Not only is she incredibly sweet and fighting hard, but she was the one my son attached to right out the shoots. I want to give her every chance possible to get well. Any suggestions?