It depends very much on how big your community tank is. If you were to add more, then another 3 would be the best amount to spread out any bullying.
However before adding any new females you will need to remove the female that is in there and rearrange your tank making sure it's very heavily planted (this gives the girls plenty of hiding places). Then you need to add them back at the same time. The girls will then start establishing their pecking order and this can take days or even weeks. Females can at times be just as aggressive as males and you need to have a back up if things don't go well. Some people have had extremely aggressive females and the worst ones have had to be removed from the group.
Also be careful when buying girls as juvenile males often get mixed up with them.