Most current poskim rule that suicide is due to mental illness (as Zahavasdad said) and not a truly conscious act of the ill person trying to control their destiny.
Learning Mishnayos Liuley Nishmas is considered a tremendous merit regardless if someone was frum or not. A tinok Shenishbar would have an especially tremendous Zechus by Torah study being done in their memory as they were not properly exposed to it in their lifetime.
Sorry about your loss and only Simchas in Klal Yisrael