Could be considered important spoilers with risk of ruining a reveal and character development:
She loved her brother, and at the same time she feared him because despite being being pretty tolerant, every time someone crossed his line he would go nuclear.
He also would always help and save her when she really needed. He would even destroy some people and force them to beg forgiveness.
She just knew to what point she could press her luck with him. Leon could always bicker and grumble but he was the one that spoiled her the most, even more than their parents, so he became sort of her hero and emotional support.
Even more revealing spoiler:
Also, she the way complains about her life going wrong after her brother dying may seem like she hated him, but in actuality it's because if he was alive Leon would never allow her to suffer the way she did.
And she lived a pretty terribly without him by her side, even after being reborn, to the point I kinda understand why she tried to take Livia's position.
@Goldreaver
Yep, the more context we get what her life was, the more we pity and understand her motivations.
But it will take quite a while for the manga to get there, we're only beginning the 2nd volume, and we only begin to see her in a less negative light by the end of Vol. 3.
I believe it should take the manga around a year and a half to get there, maybe a bit less.
Who knows what that Carla girl is planning, but at least she's going all out by kneeling in front of a man in that matriarchy. Too bad it just makes her more suspicious. Smiling and grinning while asking for someone's help to save her family is also pretty creepy.