It’s a bit forced, but then again she’s a teen who hated him for no reason, changed her mind, and immediately afterwards had their new meetcute (or whatever the word is) when he’s on top of her and ba dump. Then all her friends are pushing her towards him and she’s obviously suspect to peer pressure. Stuff like that can mess with your head. Never mind her fighting it and then seeing possibly another girl into him, provoking jealousy. Seems very plausible she would start to think she likes the guy, even if the only thing that has developed are the delusions in her head. Stuff like that happens pretty frequently irl tbh.
Not that I think the manga took that angle and if they did it’s likely the above implied and then she starts to legit fall for him as they get to know each other.
Also an important note is she’s at an all girls school.