Question: I was searching randomly on Wikipedia and I found this article on a "historical" figure called La Malinche. Since you seem to know all about Aztec/Maya culture, I'd like to know if she could be used as an ally or enemy.
I wouldn't say we know all about Mesoamerican cultures because that would require us to be a veritable corps of scholars, but we're happy to take a stab at La Malinche.
There need be no quotes around the word "historical" - La Malinche (or Dona Marina, as she was more commonly known when alive) was very much a real person and an important figure in the conquistadorial conquest and control of Aztec Mexico. An Aztec herself who went from noble Nahua family to Maya slavery to becoming the favorite interpreter and lover of Hernan Cortes himself, she was instrumental in the conversion of power from the indigenous Aztecs to the conquering Spaniards; as interpreter and diplomat she smoothed the way for demands, treaties and discussions between the invaders and the native population, as double agent she uncovered and prevented uprisings from threatening Cortes' fledgling rule, and as the lover of the most powerful Spanish man in the New World she was considered the symbolic mother of the mestizo, the Spanish-Nahua hybrid people that today make up most of Mexico's population. Many, many books have been written about La Malinche, either praising and defending her as a woman who was doing the best she could while fulfilling a traditional Aztec wife role and saving her people from more unnecessary violence, lambasting her as a traitor to her own people who destroyed their chances of fighting back against their conquerors and oppressors, and everything in between. Even today in Mexico, some groups hail her as the mother of the new Mexican people, some excoriate her as the Judas of Mexican history, and others think that all this attention focused on her takes away from the real people who should be blamed or praised for their behavior (i.e., Cortes and the Spaniards).
(In fact, if you guys want to read up on Malinche, she's endlessly fascinating. I'd recommend Anna Layon's Malinche's Conquest or Romero & Harris's Feminism, Nation and Myth: La Malinche for excellent looks at all the different ways she is studied, viewed and preserved in Mexican history, and if you'd like a fiction treatment of the story, Voice of the Vanquished and Malinalli of the Fifth Sun by Helen Heightsman Gordon are pretty fantastic interpretations, and Malinche by the fabulous Laura Esquivel is one of my personal favorites.)
As far as using La Malinche in Scion, however, I'm actually not really sure how or why you would do so. She was a mortal figure, one who impacted the affairs of her homeland strongly but who has no real mythic connotations or connections; I don't think she needs to be retconned into some kind of magical being or pawn of a god, just as most human historical figures don't. Human history is a vast and checkered thing, filled with cool people who were only people and who never claimed, aspired to or were assigned divinity, and it somewhat cheapens that history, I think, when it becomes overly fictionalized. Part of the tragic allure and complicated controversy of La Malinche's story is because it is so very human a story; she was mortal and accomplished everything she did through mortal means and for mortal reasons. Making her secretly a Scion or lesser immortal or anything of that nature robs the story of that human touch and reduces it down to merely another thing done to mortals by gods, rather than a poignant story of what humanity is capable of doing to itself, and I'd rather avoid that if possible. It's similar to making Hitler or Stalin magical (and yes, we know Scion: Companion's World at War section did this. Do not do it, it is a terrible idea) - it absolves humanity of its crimes and says that true evil, tyranny and misbehavior is always perpetrated by some outside source. It makes humanity unimportant in the very areas they should be ascendant; when it comes to human affairs, humans are fully as capable as gods of fucking everything up.
So, in most cases, we wouldn't use La Malinche in a Scion game, simply because the default setting is in the modern day and, as a mortal, she's been dead for four and a half centuries. However, if you happen to be playing around with the Aztec afterlife in your games, La Malinche's ghost could certainly be in Mictlan or any of the other afterlives you think reasonable, and PCs could definitely find her or interact with her there; and, considering the crazy kerfluffle surrounding her actions and how she might be viewed by various groups, how the death gods are treating her or how Aztlanti Scions might respond to being confronted with her could be very interesting indeed. If you happen to be playing a period game set around the fall of the Aztec empire, she could definitely be a major NPC or personality in the world; and we definitely think that her legacy, whether through the lasting effects of her actions, relics passed down over the years or even Scions who can trace their ancestry back to her, can be a big motivator in a game even if it's set in the modern era.
Also, I'm slightly loath to mention it because we are really not fans of the Keepers of the World in any dimension, but if you are using their setup from the book and have set Cortes as a Scion/god himself, La Malinche is a pretty obvious example of a mortal Fatebound to him (probably as Lover or Boon Companion), so you could explore her role in that way as well. Fatebound mortals are always an interesting place to look at for stories; they're still humans with human motivations and behaviors, but they're as susceptible to the whims of Fate as gods in some ways, and La Malinche's actions might be partly the product of her own motivations and partly the warping influence of divinity near her bringing them to surprising heights or possibilities.
The bottom line for us is that you certainly could use La Malinche in Scion, and you might get some very cool story material out of it, but that we believe it would almost always be better to do so by keeping her a human figure rather than shoehorning her into the divine.