Ahhh, así que había algo más eh.
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English tldr here:
Rinataro's words actually managed to motivate her and keep going, her hair color was also meant to be her "aiming to become a cool person", she always wanted to say thank you for returning her special notes book, as she went to do so, motivated by her friends she sees what we see in the last panel.
(her friends teased her with Rintaro being her first love and stuff as well, you people probably wanted to know that too.)