Should we get another dog?

Hello. My husband and I recently rescued an 80 pound female boxer from a shelter. We were told by the lady at the shelter not to try any other dogs with her because at one point she had gotten into a fight with a Bull Mastiff and had apparently caused some damage. However, she was said to be fine with cats and kids. Leastways, we have gotten to know her personality. "Delilah" is incredibly sweet dog and we have never seen any signs of aggression from her at all. Never a growl or a snap when the cats claw all over her. Nor, when our neighbors dogs jump our fence and decide to stay the afternoon with her unbeknowst to us. We have been thinking of getting a small, cat-sized (8-12 lb) dog perhaps as a companion. Should we?