She Does Wonder
Maybe she could have persuaded him to be better. Maybe she could have befriended him.
Minerva McGonagall ponders this all the time. The mechanics of an evil one; if someone could have helped him. Maybe he just needed love. Maybe a little more attention wouldn't have gone amiss, either.
Maybe…maybe…maybe.
Maybe she should've talked to him, showed him the love that she might have felt if she'd have known him better.
She doesn't blame herself – that would be awfully juvenile – but she does wonder.