If they have already been together then I would not worry about quarantine. There is always a chance that the new bird has something that has not shown up yet. I think if you understand the risks then quarantine is your decission.
I think that if they are already together it would stress the new bird to make another change.
As for the itching and scratching, are you sure she is not just molting. Do you think she has mites? A molt would be a likely reason she is scratching.
Last edited by BLR; 12/22/10 05:14 PM.