Females can easily be just as aggressive as males. They normally don't live with other females and prefer not to.. but it's possible to keep them together under the right conditions, as long as the owner is aware that at any time separation could be needed.
They are sorting out the pecking order right now, especially if they are all brand new together.. one will become dominant over all, and down the line to the lowest girl. There will always be chasing, why you shouldn't really have less then 5 in a tank together (tank being 10 gallons and above), to help spread out the aggression.
As mentioned before.. possibly spread out the food a little when feeding, rather then drop the pellets in one spot. Give a few inches for each one so the girls don't climb over one another as badly. Use the tip of a clean finger to get their attention if they don't see the pellet fall. Eventually they may calm down once they realize you will always give them enough, but don't expect it.. sororities are like ticking bombs... you don't know when they can be set off, exactly how it is set off, but you know it's dangerous and most of the time, at some point, it goes off and one or two (or even all in some cases) have to be separated. Just make sure there are a ton of plants in there for hiding so the food aggression doesn't continue after feeding time if one makes another angry.