yes, female bettas can fight to the extent to male bettas if they're tank is not set up properly. To set up a female betta tank, it's recommended to have at least 10 g with at least 4 female bettas in it.
To start with teh tank, it must be very well planted, with lots of hiding space and perferably no "open areas" where they can have a fight. 4 fmelae bettas is necessary becuase if you only get 2, they will fight each other adnt he stronger one will bully the weaker one to death. 3, and the two stronger ones will gang up on the weakest one, and therefore 4 will spread out all the aggression.
so, what size tank are they in and how many do you have?