Our two boys fight with each other, too. It can get pretty crazy - I can't even think of how to describe what it looks or sounds like - just imagine the tasmanian devil running through your living room making sounds like a cat fight and maybe you'll be close. It's pretty awful sounding, and whenever they do it in front of guests, the guests usually freak out.
Anyway, they tug each other's ears, they pull each other around by the tail and they latch on to legs and snouts and whatever they can. But, in spite of all that, we can tell that they're just playing with each other. We know this because one time, several months ago, one of them actually did bite the other too hard, and the hurt one made a high pitched, obviously in pain, YELP! and the fighting ceased immediately and didn't start up again until the next time they were ready to play.
So, unless your little girl really yelps in pain, and you'll be able to tell if she does, I'd say there's nothing to worry about. Just let them play fight and get their exercise! Oh, and it's our little one that usually picks the fights and is the most rough on the other, so I'm guessing Robyn can hold her own.
