I would have guessed that answer anyway because it's the only ancient Mexican civilization I know of that begins with the letter O, but I only knew about the large heads from "history of the entire world, i guess."
I was surprised too, because when I think of cartels, the first things that come to mind are drug cartels in Mexico and Colombia. I looked the word up and found out that "cartel" means any group that cooperates to limit competition from others (using unfair methods).
According to the Oxford Dictionary of English, 'cartel' is an association of manufacturers or suppliers with the purpose of maintaining prices at a high level and restricting competition. It doesn't have to do with drugs.
^ You're right. It would have been more correct to state her former names as Jacqueline Bouvier Kennedy, but I think the quiz make wanted to make it that much harder for some of us.