What size is the tank? You need a minimum of 5, so separate out the aggressive girl, and get another one. If you bought just recently, you could return or exchange the aggressive one for another I try. If you have at least 20 gallons, you should probably get a couple more so you have 7-8, so if you have to remove any aggressive. You will still have 5 or more.
I have a 20 gallon, had 5 but separated the 1 out. I’m going to be adding more decorations to see if that helps too, I have like 7 hides in there so there are extra ones for them but she was swimming to all of them when the other girls swam away