Help with lady dimitrescu boss battle!

Hi everyone! I'm enough dumb to play my first run on village of shadows so I'm having big problems with lady dimitrescu boss fight on top of the tower. I have nearly 70 pistol ammo, 14 shotgun and 21 sniper ones. However I pretty much every time use all of them against the weak woman like body and she doesn't even trigger the scene where she breaks the wall and gives me access to the stairs! Any help/suggestion is really appreciated...