female molly

I recently purchased a ballon molly “first time owning one” and I know their naturally big but is it possible she’s pregnant ? She seemed distant from my other fish and eats a lot I just want to make sure I’m prepared if so

This molly was bought two or three weeks ago and I chose her because she was a girl. Then after a week or so I looked again and thought I must have been mistaken. I have since read that it is possible for the fish to be a 'late bloomer' or even to change gender. But now she/he looks pregnant or...