Jon's wish, while both unintentional and vague, still had quite its effect. The stone's power immediately sought out a nearby woman, in this case none other than Sarah McMillian, and began to change Sarah to fit the parameters of Jon's fringe tastes.
As neither Sarah nor anyone other than Jon had heard the wish, no one would assume it was odd. Or rather, that it was odd, but that it had always been that way.
The change was practically instantaneous, with no reason to draw things out given by the wish, leaving Sarah a very strange specimen of a young lady...