One of the purposes of the X-Men over the years has been to show they’re a diverse group. Mutants can come from anywhere, and they don’t always have to be good or noble. For every Russian farmboy, German circus performer, or African goddess, there was some mutant who came from the wrong side of the tracks and was trying to make the world a better place anyway, the only way the person knew how.
That brings us to Stacy-X. She was a prostitute.