Is she pregnant or just fat?
She looks pregnant, but I have also seen some really fat Mollies that weren't. Usually when the "tummy" area gets big and kind of boxy looking (square-like) they're pregnant. I had Dalmation Mollies before and they had so many babies all the time that I couldn't keep up and had to sell them all back to the LFS!
If she is boxy looking then that's usually indication she will have fry soon. Usually this happens at night or when the light is out. If you want to save some fry from other fish that might eat them, you should buy a top floating plant like hornwort from the LFS. This provides a safe place to hide and helps feed the fry by trapping some of the fish food and providing microorganisms for them to feed on.
You will be having some fries.
Separate names with a comma.