Is it obligatory to pay the deferred mahr to the wife of my deceased brother after six months have passed since she waived it, on the grounds that she was in a state of shock?

The dowry is not obligatory to be paid to the woman after she has absolved her husband and forgiven him, provided she is obedient and of sound mind. This is because the absolution becomes effective if she is an adult, of sound mind, mature, and has the legal capacity to dispose of her property. Her retraction is not accepted, because what has been waived does not return, and if the owner of a right relinquishes it, it is relinquished. Ibn Qudamah said: "The absolution of the deceased is valid even without acceptance from him." He also said: "And if the woman waives her dowry... that is permissible and valid, and we know of no disagreement concerning it, due to Allah's saying: {Except if they [the wives] pardon it} (Quran 2:237), and His saying: {But if they themselves are pleased to give up to you a portion of it, consume it with pleasure and ease} (Quran 4:4)." It is stated in Al-Mawsu'ah Al-Fiqhiyyah (The Fiqh Encyclopedia): "If the creditor absolves the debtor, the debt is relinquished, so there is no debt, unless a new cause arises." In Sharh Majallat Al-Ahkam (Commentary on the Ottoman Civil Code), it is stated: "What has been waived does not return," meaning: "If a person waives a right among the rights that he is permitted to waive, that right is relinquished, and after its relinquishment, it does not return." Al-Zuhayli says: "If the creditor absolves his debtor of the debt, and the debtor accepts or remains silent... the debt is relinquished, and it cannot be reclaimed if the creditor regrets, nor will his claim be heard."