Firing warning shots sounds like a surefire way to start a massive battle. They would just assume you're using some magic to create sound as a distraction and charge you or something.
Itami is also basically held at swordpoint, so they can't really screw around.
Right after Rory says she's going to go crazy, the two older guys look at each other like "What is wrong with this girl?"
Then it cuts to the two younger guys who are like "What in the world is going on over there?"
Considering they probably have no idea what she's even saying, it seemed like a pretty appropriate reaction to me.