Would the girl be considered sinful for divorcing her husband after performing Istikhara and not accepting him? Is she to blame if the young man deviates thereafter? Was what happened preordained or a matter of choice? What advice would you give her to overcome this situation and choose a suitable husband in the future?

Seeking Khul' (divorce initiated by the wife) in such a case is permissible, and there is no obligation to remain in a situation for which Istikhara (prayer for guidance) was performed if something better is perceived. The questioner bears no sin for this, nor for the young man's deviation. It is advised to contact the counseling department to address the psychological issue, while the religious ruling has already been mentioned. Among the recommendations: turn the page on the past, believe that what happened was by Allah's knowledge and will, and that good lies in what Allah has chosen. Engage in religious and worldly work, and do not fear the future, along with piety, seeking Allah's help, trusting in Him, relying on Him, and taking the necessary means. Praise Allah for living in a conservative society, and know that pre-marital acquaintance holds no good.