Gome,
We're in the same area so I thought I'd forward you this URL: Adopt-A-Rott
http://www.adoptarott.com
If you're considering an adult dog, these are the people to contact. If you're considering a boy, they do have some males that are accustomed to other dogs! Please consider them.
As for how your girl would feel - please understand that there may be some 'who's higher on the totem pole' discussions. That's just nature! :) But most dogs when introduced slowly, on neutral ground (try in the park) tend to love having a buddy! Also be sure that you spend individual time with each dog so that you can maintain the bond you have, and develop the new one with your new boy.
I'm sure Adopt-A-Rott will have some techniques for you as to how to make the introductions. :)
Please let us know what you decide to do! :D