the short answer is that she wants revenge, but I can comprehend why she is so adamant for revenge
She's a pureblood noble and used to be the Sheleg's family heir before Ian came along and got their father to recognize him as his, even tho he is an illegitimate child and a former servant. So from her pov he isn't even born noble and came in and stole her role and position in the castle. Plus there's more stuff that hasn't been revealed yet.
I’d be pissed off too if I was a competent woman who had my position (which I’d been working for my whole life) taken by a man just because of his gender. (They both seem equally competent, the only difference in this case is gender)
I need to know wtf is actually her problem before I need to settle on whether to hate her or to like her. I need to understand the lil sis's motive for the tension she's causing (￣∇￣")