Doesn't she kill you on the spot if you say "if you're anything like your sister, you won't kill me"?
Yes, because
1) It's a sensitive topic for her because, well, do I need to explain why?
2) By saying that MC challenged her life views of being a superiority towards tinies, like it was in the cave scene.
3) There were not enough bond between them at that time. That's why when MC will say: "Now you look more like sisters" later on, she won't lay a finger on him for that.
There's clearly some animosity here.
If so, why didn't Kendra used Maryen's position while being with her in Homaspernia? She could do anything to torment her: take MC from her (if on Maryen's route), bring her to death colliseum, "self-defend" someone to death in front of her, but the only thing she have done was showing a public execution to plant a seed of doubt in her mind, to show her the other side of forgivenesses and second chances. It looks more like trying to help than to harm from someone like Kendra.
And yes, I consider Kendra very cartoonishly evil and petty.
Why? I mean, yeah, Kendra is not a serious character at all, but not as cartoonish and petty as Yakuu for example, with her infinite speeches about destroying your pride, learning your place and being humiliated. To be honest, I can't name any character in this game that is actually scary, not like a "fetish" scary, so what's the point in putting it as Kendra's fault?