It's a good movie, but it lacks some stuff.
First, it is unclear what kind of relationship boksoon and Min-hyuk have. We will never know who Jae-young’s father is. May be its Min-hyuk but at the end, sending that iPad isn't something a father does.

And boksoon sure loves her daughter, but when Jae-young reveal she is homosexual and tells her about issues, boksoon leaves her alone and doesn't pick up the phone at all. and before that, when boksoon went to kill that student Jae-young calls her saying she was sorry and her voice was shaking. If it were me, I would run to Jae-young thinking she was gonna do something like suicide assuming the issues she had been facing recently. and who wouldncall that much just to say her GF broke up with her. It just doesn't make sense. It's true she is facing some issues, but in my opinion, it doesn't make sense.

Despite flaws like this, and if you are looking for a good action movie the film is enjoyable to watch.