Does a female friend bear sin for imagining having intercourse with someone in her imagination, including unmarriageable kin (mahārim), and is expiation required for such imagination?

If a woman intentionally conjures up fantasies while awake, she is sinful and must repent and cease doing so. However, if such fantasies overwhelm her without her seeking them, there is no sin upon her for that. She should be advised by explaining the impermissibility of her action, and that deliberately indulging in these fantasies incurs sin. A Muslim must guard their thoughts. As for wet dreams during sleep, there is no sin in them, nor in thoughts that overwhelm one unintentionally.