Assalaamu alaykum wa rahmatullaahi wa barakaatuhu. I hope you are well. A brother is being tormented by his negligence in the past. His grandmother had said bad words about the Quran and belittled him before he became Muslim. Afterwards, he did not visit her for many years. He became Muslim close to 4 four years later and discovered that she died about three months after he became Muslim. He had not visited her nor called her to Islam before she died. Is he able to repent from this? Will she be able to take revenge on him in the hereafter? The brother is seemingly mentally disturbed due to regret because of this. Your advice is very much appreciated. May Allaah reward you.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

This brother should take it easy upon himself and praise Allaah for guiding him to Islam. His grandmother will not take revenge on him in the hereafter, Allaah willing. So he should put an end to this grief and worry and make up for what he missed in the past of calling his grandmother to Islam by striving in calling non-Muslims of whom it is hoped that they will accept it. Verily, whoever directs someone to carry out a good deed will have the reward equal to that of the doer, and if someone is guided to Islam through him, then he will earn a great reward. May Allaah guide us and him to what pleases Him.

Allaah knows best.