A lot of people are complaining about the ML. However, I still hold that the MC is just as bad.
She has a very holier-than-thou attitude in regards to the ML, and refuses to hear his side of the story. Even when she is proven wrong about the engagement, she doesn’t think to apologize for all the times she argued with him over something that was, evidently, out of both their control and is something that clearly means a lot to him.
She coddles her brother, and seemingly refuses to see him as anything but her dear, sweet sister’s reincarnation, which is quite troubling. It means she’s not really seeing him as he is - a powerful young man (he’s older than he looks) in his own right, who has basically been doing her job for years, and who is just as overprotective of her as the ML.
It’s also very problematic that she doesn’t seem to notice or care about the consequences of her words or actions. Ironic, really. She’s the one that keeps bringing up war (not the ML), even after she is informed that A. the cardinals are basically indestructible, including her brother, and thus aren’t actually in danger, B. by removing her support from the empire, she is dooming the lives of it’s countless citizens, and C. that her insistence that society bend to her rules could actually cause more political problems.
In general, she simply refuses to adapt to her current circumstances.