Quarantine should be so they are not near each other and airborne diseases can't be passed back and forth; in other words, they shouldn't be breathing air in the same area. This is so you do not infect your flock with whatever she may be carrying. She can appear healthy but be a carrier of some viral or bacterial disease. And she could be healthy, but quarantine is for observation so you can see if she shows any symptoms and if she does, you do not put her in your flock at all. During this time, you do not medicate with antibiotics. You can worm her and dust her for mites/lice, but no medications otherwise.