He's not sure. As a farm vet, he's mostly used to recommending euthanasia when these things happen,
but he did say that we could try the antibiotics! We're doing the right things, keeping her in chicken hospital and away from the other two so she can rest up.
Injection is probably a good idea, but I will try for now to get her to open up her beak.
I've also ordered online some worming treatment, in case it's that. Luckily the worming treatment is just mixed in with food.