Is it permissible to kill the husband's mother if she killed my father?

If the killing of the wife’s mother by the husband’s father is proven to be intentional and aggressive, she is subject to retribution (qisas). However, qisas is only carried out upon the request of all heirs and is forfeited if some of them pardon. Whoever pardons receives their share of the blood money (diyah). Qisas is only carried out by the ruler or his representative after the killing is proven by evidence or confession.