Ebonics is a (somewhat controversial) term for African-American Vernacular English (also referred to as AAVE); it's considered an English dialect or even a language in its own right and, as Ruth observes here, Adisa's use of it makes it clear that she's not trying to be white at all. While Adisa's desire to connect to her black roots suggests that she's proud of using the language, Ruth, on the other hand, sees AAVE as humiliating, as she's spent her life trying to speak in such a way as to sound more white. At the same time, Adisa’s ability to code switch actually gets Ruth the money she needs.