Teresa are you doing everything for Diva first, first one fed, first one let out of cage and such, after all she was there first and being a grey to boot she needs to feel she is top bird, that may be one reason she is biting you when she normally wouldn't. I have a cockatiel too and she wants to fly over on my grey's cage, might be because it is bigger than the her cage and my grey will try to bite her toes so when she is out of the cage I have to keep a sharp eye on her. I think you can work something out so that you can keep the tiel.