You can assume that all female livebearers are pregnant all the time.
They can also store packets of sperm, so they can continue to get pregnant, even if there are no males in the tank, for about six months.
On the plus side, you don't have to do anything special to look after them, or the fry. Make sure that the tank is big enough and not overstocked, that the water quality is good, and that there are plenty of hiding places for the fry. Crush up a bit of your normal fish food to feed them, but not too much; they only have tiny tummies!
We do not recommend the use of breeding boxes. They're too small for the mother fish to feel comfortable and too small for fry to grow properly.