Della was a main character in the short story "The Gift of the Magi" (1906), by O. Henry.
Della Duck was the twin sister of Donald Duck (and mother to his nephews Huey, Dewey and Louie).
Della Street was the name of lawyer character PerryMason's secretary.
Della Frye was Rachel McAdams's character, a reporter, in the political thriller "State of Play" (2009).
Della Michaelson, a character in the book "The Orchardist" (2012) by Amanda Coplin