It's difficult to say what is and isn't normal. My two sows fought for quite some time and, after having them for a few weeks, it almost seemed to get worse as their confidence in their new home grew. It did take quite a while for them to sort out their differences and one of them unfortunately ended up with a split lip and nibbled ears. Luckily, as we were about to seperate them, they just stopped fighting. Then one had to have an operation and it happened all over again, I wonder if that is because they can't remember one another? I think the dominance battle is a very individual experience for each piggie.