We just got Tia and introduced her to Sandy. I was a little concerned with how well Sandy would accept Tia, but it ended up being fine. They've already established the dominant one (Sandy) -- I sat on the floor with them when they were introduced. There was a lot of smelling and a couple of little doggy noises. Then Tia rolled over onto her back in front of Sandy and that seemed to satisfy her. Now Sandy is like Tia's Mommy. If they aren't sitting with me, they are sleeping next to each other on the doggy bed.
I would say if you feel it's getting out of hand, by all means, separate them. Some dogs take a little longer to get used to the change in their lifestyle. Just try to reassure them both as much as you can
Hope this helps a little!