How can one find peace of mind and patience in this world, and maintain humility in prayer and closeness to Allah, in the presence of a beloved person who is an atheist or doubts the truth of Islam, and fears Allah's punishment after committing major sins?

The treatment for someone who feels God's hatred for them and wishes to commit suicide is to seek the truth that affirms faith in God and to remove atheistic doubts, followed by sincere repentance and righteous deeds. For the repentant, God replaces their evil deeds with good ones, and Allah Almighty has promised those who repent that He will accept their repentance. As for those whom God has not guided, that is due to what their own hands have earned, and Allah Almighty does not wrong people in anything, and He guides whom He wills. The questioner should strive to invite her relative [to guidance] and supplicate for his guidance. She can also utilize specialized references in refuting atheism or direct him to specialists.