I apologize if this point has been brought up before, but this is a long thread.

I don't see why Lasciel would want to destroy Harry in the first place. She's the Web Weaver, the Deceiver, she's been around since the dawn of time. She isn't human, in any sense of the word. All that Harry has done so far is proven himself to be more powerful than any other host that she has ever dealt with. Keep in mind the sense of scope we're talking about here: Since the dawn of time, Harry is the only one to have not taken up the coin already.

Harry is unique, to her. Not in the human sense of the word, where everyone's a special snowflake or whatever, but truly unique, in the I've-been-alive-since-the-dawn-of-time-and-you're-the-only-one sense of the word. Why would Lasciel go for the short-term vindication of destroying someone so truly special? In the sense of scope that she plays in, why waste what is such a truly epic resource?

Tl;Dr: Lasciel plays long term. Why settle for a short-term, destructive goal?