Dean just shook his head, and when the chick raised her gun, he shot her hand, too. Dean didn't miss a second, or an opportunity. He was taking a risk that she'd fire it off as she was hit, but Dean wasn't really thinking clearly.
Years later, he would reflect on this and realize that this is what they meant by the words "blind rage."
And he just kept coming. He stopped just above the woman, and looked down at her, aiming the gun at her head. He was curious if she'd say anything, or just accept what was happening. All those people she'd killed....
Yeah. Sometimes, human beings were much worse than the monsters.