She is cute...looks like a yorkie mix to me. If you don't know much about her background or where she came from, she could get a lot bigger. None of mine stopped growing until they were about 18 months old.
Whichever one you decide on, just remember to do everything for Cooper first...feed, pet, groom, kiss, greet, give treats, pick up...everything first so that he doesn't think he is being replaced. That will probably last about a month and then it won't be so important but it will make a difference when you first bring a new furbaby home. It will also establish where he is in your pack.
I am sooo excited for you girl! You will love having another furkid!! Get out the Victoria Secret so that your partner will let you get one NOW!!