Dean looked around sharply and saw her slowly walking toward them. At first, he flinched when she looked at him, but nothing happened. Her head tipped to the side, looking almost confused. He gave her a cold smile full of fang, "Sorry. Already dead."

What could he do now? They hadn't come equipped to handle a standard ghost. No way he was running out to the car and leaving Sam with this thing. He moved between her and Sam, but it wasn't enough. He could hear Sam's heart straining and the pained breaths he was taking. Dean was half a second from grabbing Sam and seeing if Mary could outrun a vampire, but a flicker of light off a piece of glass on the floor caught his attention and...

Worth a try. He grabbed the nearest mirror, yanked it close to hold it up in front of himself and was rewarded with the gravely voice of Mary's reflection listing back her own crimes. Dean watched her start to bleed and then disappear in a shatter of glass. He tossed the mirror down, destroying it and Mary for good.