Does ongoing charity help a suicide victim atone for their sins and attain God's pleasure?

A person who commits suicide is not a disbeliever. If they die upon monotheism (Tawhid), then they are subject to the will of Allah; He may punish them if He wills, or forgive them if He wills. The benefit they receive from the good deeds they performed is up to Allah. As long as they died upon monotheism, their ultimate destination is Paradise. Allah does not let the reward of those who do good go to waste. The good deeds performed by the person who committed suicide will be found in their record, and Allah may forgive them for these deeds or for other good deeds.