I'm not surprised that Quiara used both English and Spanish in telling her story. In fact, I think she perfectly honored all the different parts of herself. While she may not know as much Spanish as she would have liked, her Puerto Rican ancestry is a very large part of her identity.
Is it also possible that Quiara provided the reader with an opportunity to feel the frustration of not understanding a language different from his/her own? Puerto Ricans ARE American citizens. However, many stores, hospitals, schools, government offices, and college admissions offices don't provided translated information, translators, or information written in Spanish. Gabi was even placed in a "special" class because of assumptions that were made about her language.