I would keep them separated for about a week or so at first. That is what we did when we bought Dutchess who was 5 years old into our family. When we were at home we would slowly bring them out to meet each other. Needless to say there was some hissing and growling from Dutchess, but Yum Yum adapted very well and loves to play with her now..They are the best of friends.
Hope things work out Nita!