It's really down to the personality of the betta. An example: we had (she died in Jan) a blue crowntail female betta who was meaner than her male companion. She killed everything we put with her. Corys, otos, mystery snails, neon tetras. She hated neons so much she would actually stalk them and shake them like a ragdoll. She was moved to a 5.5 divided tank, her male on the other side, she would try to get to him through the divider.
Now, our other females, there are 3 in a tank together. It's a 20L divided into 3 sections, males at either end, females in the middle. They get along fine. There is 1 dominant female but for the most part, she only gets mean when it's feeding time.
One thing that worked well when we were adding them was I did a water change and moved around the decor when we added a new female. That kept the dominant one off guard and she couldn't establish a territory. When we added the second, I did the same thing, then again with the third. Females can be just as territorial as the males so changing around the decor throws off their territorial markers.
On the other hand, you might get some mellow females and won't have to do this. But again, it boils down to the fish.