If she has ever been in a tank with a male, she will be carrying sperm packets and can use these to fertilise eggs she is carrying at any time. So yes, she is probably gravid (pregnant). Gestation period is around 1 month but she is already fat so maybe 2 weeks.
If she doesn't give birth in 2 months, deworm the fish because they are regularly infested with round/ thread worms. If you need to deworm them, let me know and I will post instructions.
In the mean time, feed her well, do lots of big regular water changes and gravel clean the substrate. Have lots of plants in there, especially floating plants like Water Sprite (Ceratopteris thalictroides/ cornuta), and leave her in peace. If the male starts harassing her, put him in a breeding net or another tank for a few weeks.