I've never yet seen an LFS that separates its platies, so even without looking at the photos, the chances are that yes, she is pregnant. And having looked at the photos, yes she is.
The rule of the thumb with livebearers such as platies
little boy platy + little girl platy + water = baby platies.
The best advice I can give you is to let nature take its course. Platies are baby-machines. Since it looks very much like you have a male platy in her tank, then she will have fry-drops of 30+ fry every 4-6 weeks from now until she dies or 6 months after he dies.
If you keep as many fry as you can, very soon you will be completely overrun with fish. You may be lucky and find a local fish shop that will take your fry - not all do, because platies are so ridiculously cheap from the wholesalers, and the LFS don't know whether your fish might introduce any disease into the system. If you do, then the LFS won't want to take the fry until at least 3 months old, if not older. So that's potentially at least 90 fry before being able to ship any out whatsoever. Do you have the tank capacity for those fish?
If you let nature take its course, the vast majority of the fry will be eaten - with some hiding places, some of the fry may survive, and it's lovely to watch some baby fish mature. But you won't become overrun nearly so quickly.
