Yeah, not really Ella's to blame for Mia, decision to brainfuck her was Jake's one and only, and going with "she led to the situation in the first place, so she's to blame" opens a can of worms that leads to immensely stupid claims, like blaming first man/woman on earth for all the shit that happened.
Neither it's a story for preschoolers, Ella is not a cartoonishly evil villain that does what she does becasue "I'm evil_TM", like everyone else in the story she is a complex character that has angles to it. But about that falsely accusing someone over something they did not claim - we do not know if she, to quote, prepares humanity for survival against annihilation. It might be the case, but we have no confirmation of this - Ella saying that, without anything else in game to really support it, is no proof. She is a known liar, outright stating things that are not true and easily debunked in 10 minutes of play. For all we know her plan might just be amass support of superhumans she made/swayed to her side, bring/hasten the apocalypse and rule as a king of the ashes that are left. Abused children are often, when they grow up, trying to build their self-worth on status and influence just to feel better for the pain they experienced, or use it to have the same leverage to abuse others without consequences, as seen from the perspective of their younger selves. Maybe, I do not know. Maybe she wants to bring the Apostles at person, not through avatars, to be rewarded with some turbo power boost? Maybe, it's all speculation.
But that evil/renegade and not killing for fun part? Not really true. I mean, maybe not for just fun, but she murders a hobo guy for no good reason but being mildly pissed at him. And showing off what she can do to MC, which might actually be just for fun. I don't know how many innocent lives must be taken directly, or make choices that directly lead to deaths while knowing that, for one to be considered evil, but I'd assume it's above zero. Again, she's not a one-dimensional brick labeled "evil" and that's it, the are grays here, but this is just a part of her. Like the twin slurping of Eisheth - she can, she likes the taste, so she kills.