Like what exactly is her end game supposed to be? I get that she seemed to want to get a positive response to her confession before supposedly crushing him, but towards what end and why aim to antagonize both of them to such an extent? She even admits to using Franchesca to lure in boys for her to toy with, but why all the setup for such little payoff? People can be terrible and everything, but there needs to be an internally consistent motive to explain the effort of building bridges just to burn them.
And then why does the friendship between Franchesca and Saya continue? Even if she has some sort of change of heart, this was still someone who tried to hurt someone that Franchesca cares about?