Aggressive Female Molly

[Slats]

Hi All,

I recently acquired 3 Mollies. 1 male and 2 females.

I have a problem where the black molly is chasing and attacking the other
orange female molly around and looks like it wants to fight.

The black female only chases the other female and no other fish in the tank
(glass catfish, clown loaches, cardinals and cory's).

Why would it be doing that? The male just sits and watches.

I have noticed that the black molly has a big belly. Maybe she is about to
give birth?

Any advice would be great! At the moment the orange molly is in a breeding
tank (the black one tries to attack it through the plastic).

Regards,

Slats