Balloon mollies have an abnormal bend in their spines, from what I can tell you seem to have a heavily pregnant molly, or she may be overfed and bloated. It's usually safe to assume that all female mollies you purchase are pregnant or will become pregnant. Mollies are live bearers and the females can store the sperm from one mating and have many more batches of fry from it. If you want to raise the fry you will need to set up a seperate tank as mollies tend to eat their young and any other fish in your tank will look for an easy meal. Please keep in mind you will need to find a way to house the mollies in the future should they grow to adulthood. This means having the necessary tank space or a way to rehome/get rid of them.
