would someone play a girl who doesn't think she's pretty enough, so ends up letting a very dirty man have his way with her? all sorts of devious kinks are likely to become involved. can become long term if she wants to 'stay his dirty little secret'. pbs can be discussed.
in some circles, one would think of this as a 'slam slut' or something similar. she can be married with kids but neglected now at home, she can be a college professor who simply needs this release, she can be a former model who has lost it and just wants to feel 'hot' on some level again... or a plethora of other examples that we could use.