I agree with all you've written (except the "feminine wiles" part).
This is a woman for whom her own needs and desires took precedence over her own children. Their emotional well being. Their stability and welfare. Due to narcissistic desperation and rage she conspired to murder an innocent woman and fellow mother.
I think, in fact, that the discovery that KB had a baby was something that drove her even harder to want KB dead. I think it enraged her. Because it's living proof that her man - the love of her life - was with someone else and gave that prettier, sweeter woman a child. Where most parents would feel a reluctance or pang about murdering another parent just because they feel for the child, this was one was motivated to make sure KB was eliminated, BECAUSE she had PF's baby.
And woe to little K had their plan succeeded and PF ever got together with KK for real. I don't think it would've happened (he didn't really want KK) but if it had I'm betting little K would've been at high risk for abuse and neglect at KK's hands.
My argument isn't with you. It's with the concept that she is the real killer, the mastermind, or as culpable as the actual murderer: The man who betrayed the woman he bore a child with and pretended to love and who harmed his own child by killing her mama.
ETA: I'm not sure why not believing KK was the killer or was the mastermind or even as culpable as the actual murderer (there's a reason we have different charges and sentences for different acts), is being equated as not being angry at her or not understanding that anger. Haven't all of us who disagree that she's just as or more guilty been super clear about how disgusting and evil KK is?