The general rule of thumb when adding a new cat to a household with a resident single cat (especially when the resident is female) is to pick a VERY, VERY docile, non-teritorial cat. Or...probably the best option...is to add a kitten. Kittens don't usually need to act territorial and Shadow can show the newby the rules and that this is HER house.

But, like Slick said, make sure Shadow's wishes and lifestyle are your number 1 priority. If she doesn't like other cats, its really not fair to add one.

Lots of luck with your decision! Welcome to PT, btw.

Take care,
Kelly