The most notable thing about Sally is that she's a bombshell. She's the gorgeous girl that all the boys at school talk about in the locker room. She's got eyes like Cleopatra, and she wears nylons and sexy black shoes, accessories that are, in Esperanza's mom's opinion, "dangerous" (32.4). Sally is so beautiful, in fact, that her dad says it's "trouble" (32.2).
And with a father like Sally's, being beautiful is trouble. More than trouble, actually – it's life-threatening. Every time Sally's dad catches her looking sideways at a guy, he beats her. Why would he do something so cruel, irrational, and, might we add, counterproductive (his abuse only makes Sally turn to sex to try to escape him, after all)? Well, if we were going to psychoanalyze Sally's dad based on the sparse information we're given about him in the text, we'd have to note that he's strictly religious, and that he has sisters who he feels shamed the family by running away from home. Sally says he's afraid she'll do the same thing. So we'll have to explain (but not excuse) his violent, misogynistic behavior as a product of both culture and personal experience.
The reason Sally's so significant in the book is the way she serves as a foil for Esperanza. See our discussion of their relationship in the section on "Character Roles" for details on that.
Sally's marriage to a marshmallow salesman with anger management problems and major control issues is a serious low point for the novel. It seems like a huge waste, and we're worried that the difficult circumstances of life on Mango Street might push our heroine Esperanza into a similar fate.