There's nothing more frustrating than hearing that.
In a lot of ways, Terezi feels betrayal. In a lot of ways, Terezi feels anger.
She can't forgive her. She has wanted and she has considered becoming Vriska's friend again in their time since Aradia's death. It was a blow against the girl she killed, but Terezi cared about Vriska despite herself. They had been the best of friends, back to back as Mindfang and Redglare, neck and neck while exiling agents of Derse, and Terezi has considered it a great many times.
Vriska is a brutal person, an ugly person, but she considered it all the same. She missed her and their teamwork. No one else was in sync with her that way.
Maybe she would have forgiven her with enough time. This dead girl brought back to life and thrown into prison. And maybe with time she will forgive her even after this; but that is in the future Terezi cannot see and right now, this exact moment, she is filled with an overwhelming disgust.
A lot of things come to mind, but she doesn't say any of them. She wants to scream at her and make her feel like utter garbage. But Vriska already does, doesn't she? Terezi realized that earlier, even if it feels so far away right now.
Leaving it simple would be best. Let the silence speak for her. Terezi likes to talk, but she knows when to use a silence.
She talks in a mechanical voice, feeling her body like a mechanical doll: clenched jaw, sharp elbows, pointed teeth. ]