For some reason she believed him and that confused her. The fact that she was getting more confused by the second was pissing her off. Also, the fact that he was a demon that was using his brain and not all kill kill kill and trying to fight with her was making her question everything.
"This has to be some vortex thing." She said under her breath, but she figured if he had heightened senses like the vamps from her world, he probably heard her.
There was one problem with all of this. If she let him live, he'd go and tell all of his little vampy friends about her, and they'd probably come after her.