Isabel is somewhat frail with skinny legs and large, round, brown eyes. Isabel adores Esperanza and constantly wants to hear what her life was like in Mexico. She teaches Esperanza how to care for the babies and how to wash clothes. These are things at which she is an expert, but which Esperanza has never been exposed to. She becomes a very close friend of Esperanza and seems much wiser than her eight years.
Marta is an intelligent person, not only in street savvy, but also in the ways of the political conditions both in the United States and in Mexico. Isabel does not share this interest. She and her mother were both born in the United States so they are here legally, but there is constant fear they could be sent to Mexico if they are caught supporting the strikers. She constantly harasses Esperanza and Esperanza dislikes her for it. She has short, black, curly hair, and her features are somewhat pointed. Some of her philosophy finally rubs off onto Esperanza as she convinces her that if conditions continue to worsen no one will be able to make a living there.