She was an employee of the Cyprus Harbor Yacht Club, which was owned by the wealthy Hamilton family. After the death of his mistress, Norma Rivera, Ed Hamilton began seeing Sofia romantically. The couple was first seen together when Dexter was stalking Zach Hamilton. It was his father's relationship with Sofia that pushed Zach to attempt to kill his father.
Like many characters in the series, she shares at least a first or last name with another character. In this case, her last name is the same as the "Fuentes Brothers" being Carlos and Marco. However, there is no apparent relation.