When we first got Fluffy and Eli our dog, Rosie didn't like either one. She would swat at them and hiss. She still is not happy with Eli, but we have seen Rosie and Fluffy paying at times.

I think it just takes time for them to determine a "pecking order". For Rosie, it was a month or two. I would say give them some time to adjust, and they will find their own "pecking order". It may take some time since they are about the same age.