Agreed, and let's not forget, her mother's still missing at this point. Meanwhile, Aisha's mother Lilia has already been reunited with her father... though I dunno if she will be accompanying him on his journey to find her. So she's probably also having conflicting thoughts and feelings about that... line what if her dad gets tempted and beds Lilia again? Will she have another sibling that she cannot compare to?
You brought up the fact that her earliest memory of Rudeus was when he was kicking their father's a** (so she can't equate him with the amazing older brother that their parents were telling them about before the calamity)... but then Paul forgave Rudeus and even apologized to him. So she can't process that. There she was, doing her best to cheer her father up despite missing her mother as well, watching helplessly as he keeps spiraling. And all of a sudden, here comes Rudy, who beats up/bullies her dad, but he was the one who brought back his smile. Which is shortly followed by the reunion with Lilia and Aisha, who also probably made her dad smile even more.
Now, she's trying her hardest to prove herself in the academy, while Aisha passed with flying colors despite not enrolling... and she's surrounded by expectations from professors who have seen her produgious brother's talents in action. Poor thing's probably feeling all kinds of inadequate right now
