This is how Libby would act if she had a crush on:

Kakyoin: she would act shy but at the same time she would push herself past her limits

Avdol: she would act more kind and would turn into a stuttering mess in front of him

Polnareff: she would start to speak more French and would become clingy

Dio: she would act mean to him and ignore him

Jotaro: Lol he is practically a brother to her

Joesph: no just no