A lotta people seem to be missing that her vision starts swimming and she seems to start seeing fake memories of ange saying those things. Demons in this world seem to be extremely fond of using a mixture of pointed words, a few false/suppressed memories, and a bit of amplifying specific emotions to induce and amplify strife.
It doesn't matter. She lives in a world in which it is well-known how to change your appearance, no doubt illusions are as well, and Ange is the lord's daughter and therefore a massive political target, let alone with the whole saint thing. She has no reason at all to believe anything negative she witnesses regarding Ange isn't fake and every reason to be suspicious of such things.
She also is gullible and stupid and too self-centered to even consider the obvious fact that Ange would be very busy with her training and duties. Oh, and she believes she's so super duper special that Ange would try to have her assassinated. With nothing at all to gain and no reason at all.
And because she's angry at just one person, she wants to massacre the entire city.
So, either she's being outright mind-controlled or she is simply a bad person doing bad things. If she's being manipulated, she's evil because that still means her actions and goals are her own. If she's not, then she's evil because duh.