@TheMinester You sure about that? I assure you people are way more different than you give them credit for.
For example, me. I am vastly less talented than my siblings.
I like singing, but my first and second sister eclipse me in that field. I like dancing, but my sisters are also more talented. I am quite smart, but my brother is far smarter than me. Hell, I even unknowingly repress my brother's smarter head because he copied how I think due to how close we were when we were kids.
And there are more that I won't bother telling (very personal things). Yet even with all those, I never acted like she did in this manga. Ive also met people with similar situation, and a few of them also do not acted like her.
She's just mentally weak. I'm rooting for her to die because of how predictable her character development would be.