Nenny comes just after Esperanza in birth order, so Esperanza is often responsible for her, a task she sometimes finds odious.  Nenny "is too young to be (her) friend...she's just (her) sister and that was not (her) fault...you don't pick your sisters, you just get them and sometimes they come like Nenny".  The responsiblity her sister represents makes Esperanza feel like "a red balloon...tied to an anchor" ("Boys and Girls").

Esperanza's name causes problems at school.  She says "they say my name funny as if the syllables were made out of tin and hurt the roof of your mouth".  Nenny, whose real name is Magdalena, has a nickname; she "at least can come home and become Nenny...but (Esperanza) is always Esperanza" ("My Name").

At the store, Nenny "thinks she is smart and talks to any old man, asking (the owner) a lot of questions".  She gets a demonstration of a music box's amazing sound for her boldness, however, and Esperanza has to feign disinterest "so Nenny won't see how stupid (she) (is)".  As it turns out, Nenny is even "stupider", thinking she has enough money to buy the box, which, to the owner, is priceless ("Gil's Furniture Bought and Sold").

Although Nenny annoys Esperanza, Esperanza defends her when her friends tease her for misunderstanding about hips.  She says Nenny "is stupid alright, but she is my sister" ("Hips").