Personally, my take on it is Lasciel was torquing her anger way too hard for her to be strategic about trying to lie her way into Harry's sympathies. She just wanted to burn him down on the spot, and was confident she could overpower him in a straight fight.
I mean, she was too stupidly overaggressive to even bring a shield spell to the fight. Deceptive head games seems like it would take another tier of clear thinking beyond what she already failed to show.