Responses
I think Jeanette is off-putting because she was raised specifically to be obedient and willfully ignorant. You're right that its not quite her fault, but after a certain age people generally ask questions and rebel a bit and its irritating that she's failing that. I think its especially irritating to people to people who also experienced limited freedom in their house and watching an example of a human who is okay in that environment is like...not a great feeling.
I'll try not to trash on Jeanette's naivety since it's technically understandable to trust your "dad" more than your siblings. But didn't she met him after she met Athanasia? I feel like they would have shared a bigger connection with each other than Jeanette and her dad (Who is not even her biological father).
Jeanette is not a bad person at heart but she is quite dumb and optimistic that I can't really take a liking to her. Even though she is totally oblivious to the fact that she's being use. And by Claude's cold behavior towards her, I wouldn't blame her for thinking that he used black magic. While that, Athanasia is an aldult (her previous life) so she is technically more mature and can predict things because she read the novel.
Also! Athanasia is legit cool and powerful. She's acting like an empress or a queen in her father's place!