Female bettas

Question
I have two female bettas in a 20 gallon tank, which I just discovered is a NO NO.  The more dominant one has killed everything else but the one other female betta.  The less dominant one is just barely hangin in there, even though she has plenty of hiding places.  Now the dominant female has constructed what really appears to be a bubble nest in the corner.  I can't find anything about females building bubble nests.  Neither of the two appear to have eggs in their belly.  Is there any such thing as a transgendered betta?  Or could there be some other explanation?

Answer
Amy,

Female Betta's can and do make a nest often. I have a couple that do that every now and then It does not mean she is changing genders. There really isn't anything you can do about it, it is natural. You can try adding a couple more fish to the tank to help out the one being picked on.