To be fair, it could also be that something your chickens have infected her during the move.
People tend to forget that quarantine is as much for the NEW chicken as for the old. Every flock has it's own group of little things that the flock has recovered from and might be carrying. When you get a new bird, you yourself carry stuff from your flock to that new bird, and vice versa.
If you brought the chicken in, your hens were well, and this one got sick - I'd be more concerned actually that she picked up something from your flock - or that the stress of the move made her ill. Especially since she's alone, different food, different coop, etc.
Something to keep in mind.
People tend to forget that quarantine is as much for the NEW chicken as for the old. Every flock has it's own group of little things that the flock has recovered from and might be carrying. When you get a new bird, you yourself carry stuff from your flock to that new bird, and vice versa.
If you brought the chicken in, your hens were well, and this one got sick - I'd be more concerned actually that she picked up something from your flock - or that the stress of the move made her ill. Especially since she's alone, different food, different coop, etc.
Something to keep in mind.