An Assassin's Death

I didn't understand why she was so quick to turn traitor on her organization – like yes, shortly after she is proven correct in doing so, but the initial betrayal made no sense to me. So, the fact that the guys don't trust her makes 100% sense, yet she's angry they aren't already ride or die, like ???? really? Plus, they are training her... why does she need training... they literally all worked for the same place, they should the same-ish skills that are magic-related.
It was all just way too quick for me.