Will Allah Almighty punish us for not being able to guide our sister, and what is the expiation (kaffarah) due from our parents? And what is the supplication (du'a) or prayer that we can offer to guide our sister back to the fold of her family?

Parents must fear Allah in raising their children, and indeed, neglecting Islamic upbringing leads to disobedient and deviant children.

The girl's parents must repent for their negligence in her upbringing, and frequently seek forgiveness and perform good deeds.

They must also advise their daughter and instill fear in her regarding disobeying parents, the crime of fornication, the impermissibility of her staying with a strange man, and the punishment for suicide.

If the girl continues to threaten suicide, her parents should not go to her, and suffice with contacting her by phone.

They must also supplicate for their daughter's guidance, while adhering to the manners of supplication and the times of its acceptance.