Aunt Lucia is the paternal aunt to Xavier and Yadina. She was first seen in a photograph in I Am Rukmini Devi, where she was seen as a child with her brother (Xavier and Yadina's dad) and her sister. She is first seen in the present day in I Am Alvin Ailey, where she attends Yadina's concert. She only speaks Spanish and doesn't seem to understand English, according to Yadina.
Lucia is on the left. Note the glasses.