Cause really, she is written as a bimbo, she is dumb, weak willed, has low self steem, is cheery, gullible, careless and just goes with the flow, but despite being roped together as a bully along Takae, her case is worse, cause she didnt have any bad intentions, changing stuff for sexual favors was just her relationships with men in general, so its not even bullying, its just how she operates, she never had any ill will against Saotome.
Despite this, she is the only character who has trully tried to change, not cause she stops being a slut, but because she starts putting effort despite believing herself incapable of doing stuff. And is the only one who apreciated the other girls as friends.
And in the end, i believe she is the only one who has more than 0% chance of winning over Kuzuhana.
In a way, is the only character who grows out of her original template.
(Ps: Why the fuck some of you are trying to justify an adult raping a 15 year old)