I love these questions.
It's a female, so yes, she's pregnant. Female livebearers will just about be pregnant from the time they are old enough to be sexed to the time they die unless you completely isolate them from males. They have multiple "batches" of fry in different stages of development growing at once, and can store sperm for future pregnancies. All of your females are probably pregnant, though some will be closer to giving birth and therefore are more noticeable than others. The only livebearer I had that wasn't always pregnant was a platy that had fertility problems, though the males wouldn't leave her alone and she eventually did have a batch of fry.