Okay, I'm just reading these modules as books, rather than expecting to ever play them in a game, but Cinnabar's backstory as written just strikes me as an exercise in unreconstructed tragedy.
I mean, she never had a chance!
Groups have gone to some pretty extraordinary lengths to redeem 'villains' in other AP modules: Mikaze's tale of the ongoing befriending/salvation of Laori Vaus proves he has a group made of pure RP awesome, and heaven only knows how many groups have undertaken to redeem Nualia Tobyn since Burnt Offerings hit FLGS-shelves. I know that in-character, there'd be a lot of pressure from the Shoanti to simply slay all of the Red Mantis out-of-hand during the Climactic Big Fight and be done with the whole matter... but Cinnabar is arguably as much a victim of her past as Nualia or Laori, and while she doesn't strike me as particularly forthcoming about her history, PCs are notorious for being surprisingly resourceful about such things, as well as engaging with some of the oddest people (witness the popularity of a certain giggly elven Mistress of Pain).
So I ask: has anyone's PC group ever tried setting out to show Cinnabar there are other ways to live than being an instrument of death? That in fact, there are (other) reasons to live?
While I am sure there is someone out there who has redeemed her, Cinnabar's set up is not very conducive to this. As written the party only meets her at the end fight at which point swords are drawn and combat is several rounds in. These are not the times that most parties attempt to redeem NPC's. If you wish for this to be an option, you will probably want to introduce her earlier in the game, perhaps back in Korvosa. She isn't really the type to meet the party before beginning her plans to attack them. She is more the sudden shock and awe campaign style antagonist.
I have. The party I was running it for didn't so much redeem her as I intervened. The fight played out as it did in the book, however I had the Sun Shaman step in just as Cinnabar would have been killed. I have plans for her regarding what my party may be able to do after they finish Crown of Fangs and I figured she would be a useful NPC. Currently she is living with the Sklar Quah under the guidance of the Sun Shaman.
As for the party saving her. The closest I came to aiding in them sparing her life was a sense motive when the fight began. I figured, by the description of Cinnabar, she really didn't want to, didn't care, and was generally apathetic to the whole thing. More or less going through the motions. Which they did pick up on, but the way the battle plays out it still gives you no real choice.
My group *might* be redeeming her. Our GM has heavily modified the book, and we broke into the Queen's dungeons in order to rescue a PC's father (and gained another PC who was being broken into a Grey Maiden), so we met Cinnibar early. My witch successfully hit her with a slumber hex and she made an informative prisoner who was later taken to the temple of Pharasma and got the spells upon her removed. Whether or not she is being genuine is still unknown.
The party is redeeming her in the game I'm running. (I knew they'd want to; they love redeeming people. They love Laori, too.) Given that there wasn't much written in the encounter to indicate that that was an option, I decided to foreshadow it ahead of time in two ways. In the Harrowing before that chapter, I included a card hinting that they'd meet someone who needed salvation. (I think it was The Lost, if I remember correctly.)
In addition, during the Sun Shaman's test where the PCs experience visions, instead of the aurochs vision, I gave one of the PCs a vision of Cinnabar as a child: a few flashes of her mother trying to train her, then geasing her. The character was becoming a Sarenite at that point, so I figured it made sense for her to get the hint that Cinnabar might be open to redemption.
They subdued her during the fight non-lethally and now she's living with the Sarenite PC and her family.
It actually came to pvp at my table with regards to Cinnabar. The party's magus managed to get her to her morale threshold and triggered the "event". When she's begging for death, the party's anti-paladin went "have it your way" and moved to attack. The magus tripped her on the way through to save her. He's a member of the Korvosan Guard and he wanted to interrogate her.
It got testy their for a minute and the party's took her weapons while she was freaking out and kept her locked down while she freaked out, letting her go once she was through the worst of it. Book 4 had some of the most tense RP moments in the AP (which I did not expect when I started reading it).
She's beginning to become a regular source of intelligence on the Queen's activities, but isn't interested in fighting. I'm looking at bringing her back as an ally in some of the fights in book five, but equipped with Merciful weapon enchantments. Maybe as the new Blackjack. (The mostly lawful neutral party and Blackjack have not seen eye-to-eye).
The group I DMed for spared her once she "snapped" and lost her bloodlust. They interrogated her (non-violently) and then brought her to Kaer Maga with a small pouch of gold coins to give a chance at escaping Red Mantis retribution and start a new life. One of my players found her intriguing enough to ask for her stats and backstory to use as an NPC. She now has made her way to the Stolen Lands and serves as the spymaster for our Kingmaker game
My party actually did manage to capture her and they're trying to redeem her now. She's currently living in the Dead Warrens with Bishop D'Bear and Kroft under strict observation.
One of the party members is interested in her as a romantic partner, but I haven't decided how much of an effect her lifelong trauma will have yet. As written, her turn should take time, so I'm definitely going slow with it, hoping inspiration will strike sometime in the last book or two.