To suggest a stunt for knocking Harry out:
[X] Knock Harry out, he cannot call Mab if he's unconscious and she cannot even blame him for planning it if you do it now
-[X][Stunt] With unnatural speed you skip across the watery floor. Graceful steps stealing force from the water's movement and directing you at your target. One hand drives your sword's pommel into Harry's solar plexus removing any air that could incant the dangerous name, and the other wraps around to steady him. "Sorry" you whisper as you meet his eyes.
Oh and can we really really please knock Harry out here. All this discussion about Mab this or Arawn is a diversion. We need to knock Harry out to save him from himself.
Canonically one of Dresden's disagreements with the Leanansidhe was her trying to keep him safe by denying him agency.
In a later book, Dresden almost throws down with Rashid the Gatekeeper when he tries to do what you are suggesting right here in Turncoat by knocking him out so he cant defend Morgan.
This sort of thing destroys relationships and ensures the person wont talk to you next time they're in a potential jam.
TLDR
Dont treat Harry Dresden like a child too young to make their own decisions.
He will not thank you for it.
Especially since HE's the expert here in this situation, and the person who actually knows Winter.
PS
Molly has almost walked out on her mother for making the exact same argument you are making here.
Its the centerpiece of her disagreements with her mother.
Lets not make our PC a hypocrite.
And one of her responsibilities as a ruler of winter is to enact a horrific revenge against her rebellious subject. It's called "preventative punishment". You have consistently dismissed this as a part of her motivation. This is a flaw in your reasoning. Revenge against Ankou is not just "petty sadism". It's part of Mab's duties as an upholder of the law under which Ankou has sworn his oaths.
I have consistently dismissed it because It's. Not. True.
Mab's calculus is opaque and twisty, but some features are pretty consistent.
Mab is not passionless, and she is proud. When she seeks revenge its fairly prompt, it doesnt wait for almost a century.
Over the last week I've provided repeated citations by people like her sister and the Mothers in a position to know her best about what drives her, and how calculated she is.
Mab has, by our mutual agreement, had eyes on Arawn for years. She has to have to have to have tracked Lydia's growth and age.
At any point in the last ninety plus years she could have dumped a bunch of malks or Cat Sith himself to take him out.
She could have straight up had Lydia kidnapped from school to Winter, the way Molly was.
She could have even sent the Leanansidhe if she wanted to make a point of it. She didnt.
Punishment here is demonstrably not a priority.