Sounds pretty normal. Intervene gently and only if you must. Our mini-wiener dog, Holly, bossed puppy Gromit around a lot with growling, the occasional nip, and Gromit caught on quickly. Gromit is now nearly three times her size but he still respects her space and she still gives him "what for" if he gets pushy. It's actually pretty funny to see a 12lb wiener dog bowl over a 32lb Corgi but she does it.