Ettie's refusal to cooperate is infuriating, foolish, and most of all, dangerous. Ananke can't help but blink incredulously at this man, who probably knows nothing about fighting the infected, acting like he's going to take charge and have it end well. "First off, I am not leaving this place until the operation is over, and if either of us try to run around alone, we will die. Second-" But it's too late. Ettie has already turned around and started to move.
Again.
Towards danger.
Like a moron.
"Wait!" Barking out her orders gets her nowhere, so she sprints just past him and juts her arm out in front. Not the smartest move to do to a man with a gun, but she has armor and he's probably not willing to shoot his only possible ally, so Ananke is willing to take the risk. "You don't understand how this works. You will never, and I guarantee you, will never kill an infected horde by yourself. It takes support. It takes teamwork. It takes experience. And if you run in there alone, you will have none of those things." Even the one from before didn't die until Ananke and half a dozen of her teammates had gunned it down.
"If a military soldier that's killed dozens of them before can't survive by themselves, what makes you think you will? Now, you can cooperate, and do as I say, and I can keep you alive. I can even get you to an exit if you want to leave so badly. But you have to listen to me, because I guarantee I know how the Infected work better than you do." It's not a brag, it's a fact. For every civilian in these walls, today is a nightmare. For her, it's every day. She rides out, kills infected for breakfast, lunch and dinner, and comes back home every day to wash off the blood and grime. And men like Ettie, with their big guns and bigger egos- they never understand.
This is why she hates dealing with civilians.