Let's see.
She worked herself to the bone for years, every day. Becoming an Assistant Instructor and standing shoulder-to-shoulder with Momoyo was her only goal and ambition and what she strove for since she was very young.
When that was taken away, she lost her purpose in life, and wanted to get away. Rationale was "If I can't be a Kawakami like Onee-sama and stand beside her, maybe I should try and go back to the only roots I have left."
Her intelligence doesn't make one drop of difference when emotions are involved, by the way.
And the triple-confession was hardly the peak of the route. More like something added on.
Do people go through a lot worse every day? Sure. But nearly no one worked as hard as she did for her entire life, only to find out that it was all for naught.
Also, there is no reason her character should drastically change. She becomes a little more mature, as would be expected, but is still herself. She's a strong enough person to keep going.
The only problem with the route, which is actually purely about preference, is that it's very hard to see her in a sexual light. She's just... not sexual, in any way.