either Rita is related to the girl who died or her best friend and wants revenge.
It could be she is in love with Ryu and he doesn't want her so she wants him to get his heart broken to see what it feels like.
She might even want him distracted to steal his company.
I have a hunch that the girl who committed suicide is someone from Rita's family (maybe her sister) and that's why she wants to break Ryu's heart by a stranger...but is Ryu actually responsible for someone's death??