I see some folks already calling her a brat or pissy and so on.
Just a reminder that, from Twilight’s view, not even eldritch horrors bent on destroying the world were worthy of killing. And even the worst of those could be won over or at least imprisoned without bloodshed… except maybe Sombra but yeah.
Nothing in her life or in living memory (sans the near-immortals) lends itself to taking lives as a necessary option. This is the antithesis of every Equestrian value and it’s got to feel like a massive betrayal to her for her wife and her mentor to so quickly decide to go with it.