That picture isn't very clear so I can't properly determine the platy's gender. Perhaps it is just bloated from over feeding? If so you will want to withhold food for three to four days. Here is a picture to help determine its gender.
It looks like it. Female livebearers can hold sperm for months after fertilization, so there is pretty much a guarantee if she's ever come in contact with a male. Here is a useful thread that shows what pregnancy looks like in livebearers.