Katy is startled to feel such impact from those little weapons that he is using.  She growls loudly in pain, mainly because it is a surprise and not because it is seriously hurting her, it would take a lot more than those few rounds to cause her serious harm. The confusion of the pain causes her to, instead of slamming her fists down hard on him and squishing him like an insect like she intended, she swings her arm wildly and hits him in the side causing him to be flung through the air, knocking him onto the ground, only a few inches from the edge of the building.