Katrina didn't let Kazelle's figure escape her eyes. She tailed after her without letting her know about it, masking her presence. There's no telling what that bitch would do if she gets to sniff her, that's why she made sure to not draw her attention. She waited for the right time so she could strike her without her noticing.
When it was sure that there won't be anyone who would see her, Kazelle stopped running and began walking instead. As soon as they burst into an open room, Katrina's eyes flashed dangerously. She raised her gun and aimed before pulling the trigger without hesitation.
Kazelle was oblivious that a certain agent of death was coming for her, nor did this person had been following her all this time. She wasn't prepared for it so when a sudden pain shot up from below her, her legs suddenly felt numb, and she then found herself falling.