Liz is pretty much a normal teenager, forced into the position of the saint because of what magic she can use. What Liz has been doing is basically acting like what an ideal saint should be like, in her opinion. She keeps this act up while trying to keep up with the rest of the school in terms of education. Magic wise she's top tier, but in terms of education she's lagging behind. This is why most of the stuff she's been saying before is due to all of this. Her lack of education and understanding of the situation is why people get confused why she says unrealistic ideals that won't work without a proper plan.
The direct confrontation starts at WN chapter 318.
Duke pretty much confronts Liz in the student council room about the charm magic she's been unconsciously using. It is revealed this charm magic is a side effect of Liz's unrequited love for Duke, she's been in love with Duke for some time and has been wanting him to look at her the same way he does to Alicia. The Charm Magic has been theorized to be ineffective against those with strong magic abilities and/or strong convictions.
Liz finally says she loves Duke but Duke can only give a "sorry" to her. Liz pops the question that if she met Duke first, would Duke have loved her instead. Duke says that even if that was the case, he still would fall in love with Alicia. Liz starts crying knowing her love for duke is unrequited.
Afterwards, a key question is asked and Liz responds truthfully that she was being greedy, hoping to be Duke's wife while somehow bringing peace to the world. She even confesses she does hate Alicia, never wanted to be friends with her, though mainly this was probably because of Duke being in love with her. When the idea that Alicia may have died in a foreign country cause of her, Liz cries out that she was just a baker's daughter. She doesn't understand the aristocratic world, and no one told her what would happen until now.
Duke tries to apologize for that but Liz basically says "You're the last person I would want to hear an apology from."
Liz becomes a bit emotionally unstable, she mocks herself, drops her saint act. And her real self comes out, an ordinary teenager that was in love having her love unrequited, at one point due to Duke’s thoughtless statements about himself annoyed Liz to the point of trying to throttle him for insulting the tastes of various women including herself. Liz becomes more likable as her real personality comes out. Also it is revealed that she might have been happier if she had gotten together with Alicia’s brother Eric. To which Eric, freed of the charm magic, thinks that means she thinks he’s a softy.
Also although Liz says she hates Alicia for being beautiful and smart and able to do things she couldn’t, Liz confesses she can’t help but admire Alicia.
Liz ends up having to do a tour of the school with her real personality which causes a major shift in the school. Although it might be hard for Liz, Liz says that “if Alicia can do it, so can I.”