My exalted lore is a bit shoddy but am I reading it right that Hope's group essentially a cult?
Becoming solar/Lunar means you cut ties and are inducted into a group where they talk about how you've been chosen for a great destiny, but the nature of it means you're kind of at your elders beck and call. Doubly so since they're the ones with the tools and knowledge to actually survive being hunted.
Hope was essentially sent out to prove herself then got her escort sidetracked by bloody minded vengeance. So she committed knowing the alternative was suffering the stigma of abandonment (woth whatever consequences that would follow).
It's less obvious or direct a motive. But it is a very understandable motive.
Not at all, it's more of a mutual aid society kind of thing, where there's no real obligation to bend over backwards. She was told to go bail Hound out if she could, because he was going to be cornered, and Hound refused to leave without Beacon, who would refuse to leave without getting his pound of flesh. Rather than write it off as a bad investment and just go back and go "Yeah, he refused to come back because he was more interested in vengeance than survival", which would have just gotten some shrugs and shaken heads and "Damn fool younglings", she decided that she wanted to triple down and help him out, because she wanted to look cool and important to other people so she'd be more popular, even though there was no requirement for her to succeed on this because any trip to the Blessed Isle is courting death--and getting in the path of a Wyld Hunt just asking for trouble, and just going there, doing her best, and coming back alive would have been all that was required. Now there are two dead Lunars when only one was at risk.
And so even though she had a way out, she got stuck in a fight to the death, and didn't consider retreat--or that the mortals were a threat at all when left with the freedom to organize--until it was too late. What's worse is that she
enabled Beacon and Hound rather than stand her ground, which gave them the confidence to try and attack instead of continue to retreat, or even try to do something fancy to shake their tail or split the attention of their pursuers enough to have a chance at winning a reversal. She had the bargaining power there, not them, but she forgot that because she wanted to suck up to Hound and go for a Perfect Win instead of focus on actually living.
So no, her cardinal sin was getting stuck in on a doomed last stand that she had no obligation to get into, and then dismissing the threat of the people she already wrote off as meaningless trash, so she took a bad hit when she broke to escape, and from there it was curtains because she had no way of recovering from getting surrounded by a horde of mortals and stabbed until she died.
All because she wanted to be more popular, and didn't take the other side seriously because they were Beneath Her.