The point is she failed. Her shadow fell in love with Harry and took his side and helped him.. The moment Lasciel's shadow truly becomes Lash, not just Harry's nickname for her, she says pointedly, softly, shaking her head, "She doesn't deserve you.." So not just Harry scorned Lasciel, but her own shadow did. Also remember what distressed Lasciel/Lash so much was when her host Harry died, she died.. So the fallen angel's revenge wasn't just on Harry it was on her shadow, Lash as well, both scorned her.
All the examples of whispering Vairelome posted happen after White Night. After Lash has sacrificed herself. After Lasciel's coin was dug up from its place in Harry's basement. Lasciel found out what had happened either at the moment the circle was broken (since Lash is still there she'd have had a link, albeit a weak one) or after she was recovered by Nicodemus (if she was).
No, we have no facts, it is never said that it was, those are merely guesses. Since Lasciel's shadow had been doing all of the whispering and she got transformed back in White Night, she also got transformed into Lash by her love for Harry. She became independent of Lasciel, there is evidence shortly after in White Night when she says "all that I can my host..." after Harry plays and just before he digs up the coin and gives to to Father Forthill, that Lash whispered to Harry. That wasn't Lasciel, we also have the WOJ if you believe him that the only appearance of Lasciel after that was in Changes.
It's not being said that Lash was the one doing the whispering. We're saying that after Lasciel's coin was unburied she became the one to whisper in Harry's ear the depressing thoughts that have already been posted.
Oh Lasciel did appear in Changes and was the whispering shadow we see in GS. My argument is she is not the one who is whispering anything to Harry in Turn Coat.. There is no evidence of it.
There are educated guesses. The series isn't finished so we can't look back with hindsight, only post our theories from the evidence we have in the released books. This seems like a semi-solid theory to me with decent evidence to back it up.
Except back in Death Masks through to that point in White Night, she was trying to seduce Harry to take up the coin.. He didn't, in the cave in White Night, her shadow tried desperately to get Harry to take up the coin, to save both their lives. Harry refused.. Then Lasciel becoming Lash, says " she doesn't deserve you." At that moment the fallen angel Lasciel became the woman scorned. Not just by Harry, but by her own shadow because of Harry. At that point she wanted them both dead. And yeah, revenge is a dish best served cold.. She waited, till Harry reached his lowest point, along with facts he could not argue against.. 1] he was helpless. 2] He was little Maggie's father, while how she got into trouble maybe wasn't his fault, the fact that she was in the world, was. "And it is all your fault.." Those are not the words of seduction, those are the words of revenge.
True enough, we're just arguing that Lasciel possibly whispered more than once. Think of it as following a marked path to a river, rather than hoping to find an oasis. Chances are Harry would have found himself at the lowest point he could at some point, and Lasciel would be there, but it's also true that continued whispering would make him more likely to take the course of action that would result in his death. Besides, it fits Lasciel's MO to give subtle nudges every so often, rather than one big strike.