is the character round or flat?

I'm going to assume you're talking about Esperanza here.... and yes, she's ROUND, we know a lot about her. Esperanza is the "heart" of this story. She's not only our narrator, but both the protagonist and antagonist as well.

Over the course of the novel she changes drastically, and the reader, in turn, experiences all of those changes right along side of her. Because the novel is written in fragments, we not only learn about Esperanza from the things she shares in her own perspective, but also through the stories the other characters share.

If you are referring to the protagonist Esperanza Cordero, she is a round character. Throughout the course of the novel, Esperanza invents the person she will become: she aspires to be a writer and to overcome the limitations gender, race and class has placed upon her.