ok, I would agree it is most likley dominece, females can be like that. dominant females really need to be paired with submissive ones. I have several dominant females, and I never ever house them together because they can get very nasty. I would reccomend getting them each a new friend, but you will need to study the issue and find friends that are calm and docile.

you COULD try to split tank them back together, but there is a good chance you will go through this again if you go that rout.