Ga-min should teach the teach how to use her fists and common sense. What sensible person would do in this case of open door? Called and waited for Ga-min or other buff person or even policeman and sent him in alone. Frail and intelligent girl and yet so dumb. Some people are unnecessarily evil, they exist, If you can't make them not to exist you should be wary of them at least.
But you know what's the best in this situation? If you live high enough from ground you can block the door and use some home made smoke, so they'll try to escape and that's when the police you've called beforehand comes in. Gosh, I should've studied chemistry in school, college instead of physics...
Moral of the story, if your door is open and you remember you've closed it use your brains for once and get help depending on the situation.
P.S. Smoke part is just a joke, no way you would carry it in your bag or make right away. Also this could be deemed excess of self defense or even worse.