I don't think Kanae is going to do something bad to Tomiko, and I think that based on both of their characters, Tomiko will found out what happened to Ichika and she'll tell Kanae about it, and that's where things will go south.
Kanae has a twisted since of morality because of the environment she was raised in where the punishment is disproportionate to the crime, but I don't think she's a sadistic entity (if you remember her facial expressions during that scene, she was stern and serious and was not enjoying herself.) nor a malicious one per se.
Tomiko is heavily influenced and pressured by those around her because of her fear of being alone, which Kanae can empathize with, and I don't think she would turn against those roots unless prompted to by a sense of betrayal.
Probably the rape scene having consequences on Kanae's relationships into the future and her new-found clique would probably be the natural consequence of the actions taken.