azygous she is beautiful! And I hope she makes it. You are doing all that anyone can. The feed supply may be able to help with dosages for the birdie. If the others are healthy, I don't know if I would treat. The ONLY reason I say that is from my previous post about cocci. It is likely everywhere, with most all birds. Most are able to build up an immunity to it if they are healthy and have good functioning immune systems. If you use the antibiotic, it can cause an overgrowth of other bacteria, fungi and yeast. I think antibiotics are only needed if there is an imbalance. In the healthy chicks, there is balance or they wouldn't be healthy. If it is wiped out now while their immune system is forming, they won't develop a resistance to it and can be wiped out later. AND antibiotic use will not totally wipe out all bacteria. The ones that are left develop resistance and that's how you get medication resistant bacteria. In the sick chick, it should wipe out enough to help her not be overwhelmed by it. Hope that made sense. However, IF ANY ONE SYMPTOM should occur in any other chick, I would treat all immediately! There is a fine balance between being colonized with bacteria and being overwhelmed with it. And it can happen quickly in delicate babies of any species with developing or weakened immune systems. Most of what I'm speaking of comes from my knowledge of humans, microbiology and the disease process. But I believe much of it translates to animals. Some things are the same across the board. If you have an avian vet you can call, I most definitely would not hesitate!