i love your idea, especially the end - the fact she still is one, awesome
I see it more like this:
At the beginning we see David and her were in a relantionship and after a while she tried to kill him, like she did with all the other men, but didn't finish her job - leaving him almost dead.
Some time passes by and David and the rest of the band are hunting her down and they're trying to kill her. They finally find her, in a very deep long cave, with walls covered in blood and ocassional candles, making the place even creepier, lights flickering, shadows forming etc.
At the end of the cave they find her - long red hair, yellow eyes, dressed all in black, levitating above the ground. They start to fight her but she knocks them all down - when they wake up they're all in chains on the walls of the cave.
The softer/deeper/guttural part of the song is when we think David is trying to plead with her but actually he's drawing the attention away from the fact that he's freeing one of his hands. He frees himself, quickly grabs a dagger from his jacket and stabs her in the heart. She starts to burn from the inside out and then turns to ash.
Then the guys start walking out of the cave, putting c4 explosives on the walls. Once they are out, we see them walking away, Dan pushes a button and detonates the explosives, destroying the cave and burying everything inside.
hope you like it - btw, where should i post this and other ideas? in the third podcast thread?