Use the flashlight! Hit her! A Lot!
From Create Your Own Story
Melanie is screaming now, unsure of what she's seeing. You don't waste time explaining or waiting to see what this thing is going to do. It seems violent. Excessively so.
As it attempts to get to it's feet, you swing down with the flashlight and bash it across the back of the head. It's face slams down onto the floor, and blood spatters every where. You hit the woman a lot harder than you thought, but you aren't taking chances. You hit her three more times in quick succession. I mean, she was having sex with a dude she probably murdered. Better safe than sorry.
You check around the room for anything of use, and find their guns on the floor, empty. As you glance around, it looks as if someone just shot off each and every round randomly. You do find a night stick and a taser with a single shot left, so it's not a complete waste. You give the taser to Melanie and take the nightstick for yourself.
Going back out into the hall, you shut the door behind you and calm Melanie before moving forward.