Will the wife who invoked a curse upon her husband—due to his oppression of her—then he died a week after her supplication, be sinful, and will she be considered his killer?

The supplication of the wronged against the wrongdoer is permissible, though forgiveness is more virtuous. This permissibility is indicated by religious texts, such as His Almighty's saying: "And whoever avenges himself after he has been wronged - those have not upon them any cause [for blame]," and His saying: "Allah does not like the public mention of evil except by one who has been wronged." Also, the Hadith (definition) states: "Beware of the supplication of the wronged, for there is no barrier between it and Allah." The virtue of patience and forgiveness is indicated by His Almighty's saying: "and that you pardon is nearer to righteousness," and "And whoever is patient and forgives - indeed, that is of the matters [requiring] determination." The wronged person should not exceed the measure of his wronging in his supplication, for "whoever has assaulted you, then assault him in the same way that he has assaulted you." No one can assert that the death of the wrongdoer was due to the supplication; knowledge is with Allah.