Sadist??
Against Ono’s mom, she was fighting for Akira and Haruo’s sake. with the worst character against the strongest. She had no leeway to play nice. Also, haruo was at stake. she winning by crushing Ono-sama was her way to say that she didnt want to be Akira’s replacement in Haruo’s life. She loved him enough (which he never deserved in first place) to protect his love for Akira.
Against Felicia, they were fair fights between two friends, and the best one always won. Felicia didnt retire because Koharu-chan crushed her, but because she lost the “Alpha” position in the group and the boys started to flirt with her, and that annoyed her. That’s why they are still best friends after so many years.
and Arisu… that punk was a grown up guy using his money to bully kids. Koharu just gave him the beatdown he deserved.
And now, she is not trying to humilliate spice, but trying to rescue him fron his own darkness.