I don't buy that Venat wouldn't try to stop the Final Days. She's the former Azem, and doesn't play by the rules, being Chaotic Good and all.
Perhaps there was no time to convince anyone else to do otherwise; perhaps she tried, but the End of Days were already there.
Assuming she could think of no way to reach the Meteions, she probably couldn't stop Zodiark from being summoned; and then she probably thought it was the right thing to do to become Hydaelyn and do the Sundering.


Later on though ... my personal head-canon is that she DID try to stop some of the tragedies we told her of. Starting with the First Rejoining. Which lead to that whole situation with the 13th and the Void.
Going to go out on a long limb here and guess that her saying "screw causality" is what summoned all the Voidsent; not just having too much dark aether.
Which would explain why she never intervened again, not even to tell us things in ARR, HW, StB, ShB and early EW...

As a corollary, it would mean that G'raha's own complete disregard for causality should be coming to bite us in the butt any day now...