What should a wife do who made her husband swear to divorce her if she gave birth to a girl, and she did give birth to a girl and placed her on a train out of fear of him, and now feels guilty about her daughter whose fate she does not know?

The wife must perform sincere repentance, seek forgiveness, and ask Allah for pardon. The rulings concerning killing and causing death, such as blood money (diyah) and expiation (kaffarah), do not apply in this case because the child's condition is unknown, and the default is innocence of responsibility. Wealth is forbidden unless by certainty.