Vriska did absolutely nothing wrong in that entire exchange.

And you're going to sit right the fuck there and listen as I tell you exactly why this is the case.

Terezi began that confrontation by negating any claim of credibility that she actually had. She accused Vriska of serial murder and supported her claims with evidence so lacking it essentially didn't exist at all.

If someone lied to you and accused you of things that you didn't do, would you assume that they knew what they were talking about regarding anything thereafter?

Furthermore, this was the first time that Vriska ever disregarded a prophecy, which I might add is something important for her growth as a character.

But the fact that Terezi ruined any claim she might have to know what she was talking about is just the start of how she fucked up that meeting.

Although her warnings were worthless since they came from the mouth of a liar, they weren't even accurate. Terezi's phrasing heavily implied that Jack would fight her before anything else. Essentially just meaning that she had to win, something she was already well aware of.

Terezi did not say, nor imply that Jack would ignore her in favor of murdering everyone else and blowing up the meteor. Which is an incredibly important distinction.

Of course the fact that Terezi couldn't be trusted is just half of how she ruined everything.

The other half lies in how she actually handled the situation. And it is incredibly clear from the start of that confrontation that Terezi always intended for it to come down to murder, even before she knew about Vriska's intention to fight Jack Noir.

Terezi couldn't possibly have been stupid enough not to realize that antagonizing Vriska wouldn't have any possibility of actually convincing her. And given her propensity for manipulation she should easily have been able to figure out some method other then "murder" in order to prevent Vriska's leaving, were she so inclined to actually do so.

But no, Terezi just drove the whole fucking thing into an idiotic "Live or Die" decision by Vriska, knowing full well what would happen ahead of time, realizing only at the last second that she didn't want Vriska to die, then being forced to do it anyway because of her own hideously poor foresight.

The fact that Terezi had to kill Vriska in order to save everyone else is no one's fault but her own. Vriska had no intention of doing harm, was not warned of the possibility in a credible fashion and continually antagonized and manipulated into a conclusion that was to Terezi, inevitable. I literally cannot think of a single thing that Vriska did wrong during that confrontation. Ignoring the advice of a lying seer? Disregarding warnings phrased in such a way as to be utterly meaningless? Reacting to hostility with hostility in turn? What exactly was the fucking crime committed here? Unintentional Ignorance? Distrust of the dishonest? Tell me, I'm fucking listening.

This is part of the reason that I'm not at all happy with Terezi right now.