Through a combination of coincidences, namely Faust stepping to the side when shooting and Arthur and the roach on his boot moving around trying to get away from each other, said roach is suddenly directly in front of Charlie´s feet.
Instinctively (and completely forgetting about her wrench) she steps on it as hard as she can.
1d20+2+5=10
1d6+2=4
Even though she could have hit it better, it does the trick. The shell cracks with a nasty sound and roach-goo splashes everywhere. When she´s sure the thing stopped moving, Charlie slowly raises her goo-covered boot out of the critter´s corpse.
"Yuck..."
She attemps to get rid of the stuff by shaking her foot with less success than she would have liked. Well, at least it´s just the boot. Following Arthur´s example from earlier, she starts scraping the rest off against the wall. Charlie looks around, breathing out in relief. All of the attackers are dead now.