So I guess, as some had imagined in previous chapters, his father killed her parents. However this would not be a motive for revenge because he did her a courtesy by killing them.
Only one thing seems strange to me, if she really lived in that closet without any knowledge of the outside world, this more than suffering should have caused her alienation, i mean, she couldn't have realized that that life was wrong, but for her it should have been the normality