Ohh, interesting take! I haven't actually read Blood Meridian, but I know a little about it.
Marcy only has a few very loose inspirations, such as the Leper in Darkest Dungeon and Slade from Teen Titans. I basically wanted to avoid making an orcish stereotype, so I went with a kind of "samurai meets bandit" blend of traits; composed, noble, and even sympathetic at times, but she's just as much vicious, pragmatic, and vindictive.