Sundering stuff established in the Q&A

[Brinne]

Not just Ktsis, but before that. Her entire goal once we told her the future was that we were trying to figure out how the Final Days happened in order to avoid them. None of the three ancients, Venat included, accepted the Final Days as a foregone conclusion. She even sounds like she has plans to continue to try to avert them after the memory wipe, though I'm sure at that point she was also thinking about how the Hydaelyn plan could be put into action. But, yes, before that she was trying to avoid the apocalypse and therefore avoid having to sunder anyone.

Yes, before she hears our stories of the future, and before she hears Meteion's report. Venat herself states that something drastic must have changed her mind, since her initial instinct is to, yes, stop the Final Days altogether - and she notes that that doesn't seem to be the priority of her future self. After getting to know us and hearing Meteion's report:

Regardless of how we proceed, if we are to permanently avert the Final Days, we must be equal to Hermes's challenge. We must prove that mankind is worthy to exist. And this hinges, I think, on how we confront the all-consuming despair that accompanies a senseless and seemingly inevitable end.

She fundamentally actually agrees with the premise of Hermes's test, that mankind's right to live is not a given, but something that must be "proven." And she decides that worthiness will hinge on subjecting them to absolute despair and seeing how they respond. In this moment, she more or less strongly implies that's made up her mind to allow Hermes's test to happen, and her strategy is to do her best to prepare people to simply endure it - which is even symbolically reflected in the montage, where she walks past the first Ancient being killed and does nothing to interfere.