I agree with what you said about her being ignorant/ too innocent even if she didn't meant bad, but she just truly doesn't understand enough to be saying those things. However, I see that scene as both being ignorant because just like she doesn't understand where his struggles come from, he doesn't understand lavi's struggles and for him to come and just discard it as "oh he is just a monster you're showing compassion to, and doesn't matter why he killed so he is a monster" is ignorance from him and in a certain way hypocrisy.
yeahhhh, they both don't understand their shortcomings and how their words are contradicting them. His words are posting a judgment as if he understood everything while at the same time he is clocking stella for, and stella is trying to show compassion and understand but her words are doing the opposite and passing his comfort zone without him wanting to/ giving a right to. However, like u said, they're not doing it on purpose.

I am an extremely weird human being that enjoys reading incest. Not when its forced upon though, I draw the line at forced intercourse between inner family relations. The Prince and his behaviors makes sense and I understand to some degree how it feels given my own experiences growing up, only differences was that... mine was other children trying to get into my panties and not blood related to me. So I am able to understand where he is coming from. The FL is coming on too strong with trying to be understanding and help him but she is far too innocent to see where his struggles truly lies gence being called ignorant. Harsh but true, she means well but prying into matters she doesn't know too well is going to far.