Was she just added? Sometimes if the sorority is already established and you add a new female, there is a sense she is not part of the group and can be violent and defensive, which goes away one she becomes accustomed to her surroundings and all the girls get used to one another. Just keep on eye on them.
If it is very violent, you can try a "time out" I call it. I float the aggressive female in a clear jar or small tank in the sorority so everyone can get a look at her and she can get a look at everyone else. Sometimes I keep her in there for a week, replacing the water with tank water twice a day so it doesn't get bad. Then release her after a few days or a week. You can also rearrange a few decor items and/or add more plants.
In the end, like Vil said, there are some females who need to be alone. Trust your guy so no one gets hurt!