Okay, here's the general check I'm going to suggest (to be applied in any situation):

1. Is this important to the story?
2. Is this an important part of the character?

If it's not, you probably don't need it. I could have Saphira bring her squirrel or some other animal with her, but it would only be more clutter. Ruby could have connections in the town already that would give her more access, but that would just be making her a more powerful character without reason. So if your companion is important, there is a way to make it fit in. If it's just "bring it to scare Mizzie even more," then you don't need it.