I Thought Savathun Was Smarter Than That Honestly… (Spoiler Warning!)

Again, Spoilers for those who are so inclined to avoid them!

So, she does realise that isn’t her brother? We have Oryx’s corpse in vanguard custody. This echo isnt him, it’s a Paracausal snapshot in time, nothing more. An imitation. Her actual brother is dead. It’s no secret that Xivu Arath is a total hypocritical moron but Savathun is supposed to the smart one here. Am I missing something here? If I were her in this scenario I would be actively offering to help the guardians destroy this echo for daring to imitate my actual beloved sibling.