Is it necessary to kill a girl who has committed an abomination (honor crime)?

If a girl commits an "honor crime," she has fallen into a grave sin that requires repentance. It is not permissible to kill her except by the Imam or his deputy, after she has confessed to adultery or if four trustworthy witnesses testify against her, provided she was not coerced. In such a case, the prescribed punishment (حد) is carried out: stoning for a married woman (muhsana) and one hundred lashes for a virgin. No one other than the ruler is permitted to carry out the punishment. Whoever kills her shall be killed in retribution unless the guardians of the blood forgive him, unless she was a married woman (muhsana), in which case he is not killed for her nor is he obligated to pay blood money, but he must provide proof of her voluntary adultery. He is sinful for overstepping the authority of the ruler. Her family may discipline her wisely, without violence that could worsen her situation.