Generally looks like people don't like switching to archetype progression, and having given it some consideration, I concur. Whether or not it's more 'balanced', this is intended to be a Path of War campaign, so only giving Harbingers 7th, 8th, and 9th level maneuvers doesn't really fit what I'm going for.
Her Stolen Fury Trait comes from, not the suggested ritual in the Players' guide, but she was a virgin sacrifice and was raped by an incubus when she was 16. Which is how she uses Black Seraph, the demon seed she absorbed infused her with the power to use it.
While it wasn't the exact ritual suggested by the Player's Guide, I will note that in order to have the Stolen Fury trait, the character must have been tainted by a ritual by demons or demonic cultists that was disrupted or interrupted before reaching completion. Violation by an incubus can count for that, so long as it was part of the ritual. Otherwise, Exposed to Awfulness would be appropriate.
The same applies to Tevreh and the demon that she survived an encounter with in her backstory.
I had an idea that later she doesn't go mythic like the rest. she instead uses a mythic wish to become a mythic Erinyes or something, because her hate of demons is too strong. If that were even possible.
It would be a pretty challenging finding someone (or, rather, something) able to cast that mythic wish and willing to cast it for her. And it seems very... odd to make a wish and go straight from a Chaotic Good worshipper of Gorum all the way to a Lawful Evil erinyes. I'm not saying it's impossible – but it would probably be an endgame / late-game side-quest.
That said, the Hellknights, an knightly order modeling themselves after Hell itself, prizing law and order above all else, are a presence within the Crusades. Though there are more evil Hellknights than good Hellknights, they accept lawful good, lawful neutral, and lawful evil characters alike. I was thinking they probably were among the most common practitioners of Black Seraph among the Crusaders. If you decide to give her a more lawful bent, you could have her join them.
Due to last-minute amendments to party composition preferences, I will be dividing you into a trio of campaigns, three characters each. ShadowFox89, before I can finalize these parties, I'll need you to select a campaign trait and commit to which mythic path your character will eventually walk.
Later tonight I'll be going through character sheets again. Once the campaign groups are set and at least one group has their backstories and character sheets sorted, I'll start working on getting an opening scene up.