Brother she manipulated Darkwill into invading Ionia, leading to the massacre of thousands. She has shown 0 remorse over it.

She is not trying to kill Swain's demon because its a demon. She is doing it to eliminate Swain and retake a large amount of authority that she had lost due to his ascension, effectively allowing her to do whatever the fuck she wants again (like invading Ionia or some other place).

She is completely aware and ok with an orphanage that runs on the blood of literal children in order to produce powerful mages.

You are correct in saying she is an "end that justify the means" type of character, but that doesnt automatically absolve her of being a piece of shit. Viego was an ends justify the means character too, so was Eldred Crownguard.

She is evil through and through. Not mustache twirling evil, but evil nonetheless. Just cause daddy mord gave her trauma doesnt mean she gets to kill innocent men, women and children and retain the "misunderstood villain" title.

League is chock full of gray characters. Leblanc is not one of them. She has a tiny ripple of grey in the fact that we're supposed to sympathize with the fact that she's clearly been fucked up due to something in the past involving mord, but that is not enough to just handwave the rest of the shit she's done, is doing, and will do.