That's what happened when I got my 2nd cat. The older one was cautious and now they are happy playing with each other.
She grew up to be about 10 pounds. She was discovered under a porch during a hurricane we had in DC a few years back and the shelter had a tough time getting her adopted because she started off as half-feral. We felt sorry for her and decided to give her a chance. Our older cat was becoming bored and lethargic, and he needed a playmate.
It's worked out pretty well. As she's gotten older, she's relaxed a bit. She did, however, nab a bird on the deck a week back.