How will adding another bird change Nell's personality? The Grey lives with a cockatoo. She may show some jealousy at first. Make sure to give Nell special attention and treats, try not to change her schedule for the new bird if at all possible and she should learn to be accepting.

Being this bird is coming from a home enviorment how long do I need to quarintine the new bird? I would suggest 60 days as being the best but at minimum 30.

Should I have any tests done on the new bird, The owner claims she has always been very healthy. Definitely have tests done. Since the bird has always been "healthy" more than likely it has never been checked and if nothing else needs a full blood work up. Birds hide sickness so without ever getting them a checkup how do you know if they are healthy or just hiding symptoms. It would be terrible to add a new bird just to have your long time companion get sick because the new one was carrying a disease.

Will they ever be able to be together on the same perch? As long as they show no aggression of coarse. If they don't show aggression and are very well supervised then they can be introduced outside their cages in a neutral place. If the stand is Nell's special place I would suggest getting a new one before any introductions so that Nell will not be territorial over it. Or even make you own playgym where they can play together or on opposite sides to be away from each other.