That’s true for understanding her I just take mainly the scene where all the siblings go to classes and hold political debates with Clara’s father,there you can get a peek of her character.
Her pragmatic and harsh judgments,like no matter which option you choose on the War of the Brothers scene,Atherys just stays put on her own opinion refusing to make any kind of reflection about the matter,that stubborn character willing to ignore your closest advisors that’s her worst Trait the one that truly pushes her away from being a wise ruler.
Here,remember uncle Tywin’s wise words.
"A wise king knows what he knows and what he doesn’t .You’re young. A wise young king listens to his counselors and heeds their advice until he comes of age. And the wisest kings continue to listen to them long afterwards."**