Although she's not around for much of the book, Nacha is a driving force behind Tita's strong character. She's a mother figure, a bosom buddy, a Top Chef Judge, a guardian angel, and a mysterious indigenous woman all in one.
When Rosaura is going to marry Pedro, Nacha's the only one to comfort Tita:
Now we're alone in the kitchen, so go ahead and cry, my child, because I don't want them seeing you crying tomorrow. (2.96)
We think it's super important that she refers to Tita as "my child," because without her, Tita wouldn't have a positive female role model or know the meaning of familial love. Perhaps blood isn't always thicker than water.