Who is Zulema from I, Juan de Pareja and what is their importance?

Zulema, a beautiful black woman, is Juans mother. She is a slave, who works as seamstress for Dosa Emilia. Zulema died when her son was five-years-old. Her legacy was to her son consisted of two earrings, golden hoops that Juan cherishes. Zulema is described as tender and kind.