I had a sorority of 4 girls too. 3 of them were perfectly fine in there together, but there was a red one that constantly fought with the blue one, even in a heavely planted tank. I had to take her out and tried reintroducing her several times, but it never worked out.
Some females, if they are relatively large and around the same size, will fight until one is dead in order to claim a higher position in the pecking order.
Right now, the blue one and the orange one(unfortunately, the other 2 died) live in a 25 gallon and are BFFs. I would recommend getting more though, especially if you have lots of space for them to hide in.
Where mine is a 25 gallon, they have more room to get away from each other, but in a 10 gallon, I recommend getting more or like Myates said, it could get aggressive.