Yep the majority of female betta's can be kept in groups of no less than 3/4, I have an all female tank with 6 females and there is a pecking order with a little bit of fin nipping but no major problems. Just give them plenty of places to hide and they will be happy.
They can also be just as agressive as males and will have a pecking order so be prepared for nips! I had a female community for some time but got fed up of the constant battles and divided them