Sheba and Mia used to be friends before I got Mia 16 months ago. When I got Sheba as a companion for Mia, they were friends, but Sheba wants to be the dominant one, and Mia's okay with that. So, for the first week or so there was some sorting out. Sheba is still dominant, but that stuff has given way to them being really good friends now. Their play doesn't involve dominance anymore. I think Sheba actually respected Mia more after this torpedo attack:
Now they're well on their way to being besties, which is what I wanted. Today at the park: