I remember being nervous about how Bella would react to having a baby in the house when Christian was born. Happily, she's never given us reason to worry in the nearly four years that Christian has been with us.
Our "two kids" actually get along quite nicely! He likes to call her up on our bed, says "Hi, Bella!" to her when he comes into his room, and likes to throw her toys for her to chase.
He laid down next to Bella today and told her, "Lick me!" She's not a licky kind of dog, but she oblighed and gave Christian a few licks ... and he loved it! "Bella's licking me!!" he squealed.