If she had been in with them previously, and she's the only one who got "suddenly ill", I would think that your toxin theory is probably correct. She probably got ahold of something that the others didn't, or got the lion's share of something that everyone else only had a little of.
The only reason to keep her quarantined would be to make sure that she has fully recovered and is strong enough not to get picked on by the other chickens. Good luck!
The only reason to keep her quarantined would be to make sure that she has fully recovered and is strong enough not to get picked on by the other chickens. Good luck!
