So how DO you kill her? She can't be immortal, because that's stupid. Besides, how would she live without a brain? That's the thing that tells her body what to do. Without it, her body would breathe, meaning it would suffocate. And if you're saying she'd survive without breathing, then I take issue. You might have made Light's healing too powerful. Hell, even Wolverine dies without his brain. Actually, it's the only way to kill him.