We just went through this last month when I brought Doodlebug home. I had the illusion they would immediately become best buddies. Pebbles was so stressed. It broke my heart and I cried.
She would looks at Doodlebug and yap (not bark) and was drooling and spitting bubbles. I slowly got better and they are usually pretty good together now. Pebbles will give an occasional good nip but IMO its well deserved when she does and stops him from being obnoxious. I do not leave them alone togther when we are not home. Things will get better. It's like bringing how a new baby and telling your toddler that you have to share mommy and daddy!