Is the woman who hit her nephew considered sinful for hitting him, thinking that he had taken the headphones, and what is the expiation for that act?

The fundamental principle concerning assaulting a Muslim by striking is its prohibition, unless specific Sharia (definition) conditions and regulations for its permissibility are met. For instance, the disciplinarian must possess legitimate authority, the striking must be for the purpose of discipline and not revenge, the person struck must have committed an act that warrants striking according to Sharia or custom, the striking must not be excessive, and it should not exceed ten lashes. Furthermore, the face and sensitive areas must be avoided. If any of these conditions are not met, the striking becomes an act of aggression and injustice, necessitating repentance and seeking forgiveness. However, if the error was unintentional, there is no sin. In both cases, compensation is required if the struck person sustains harm.