She was the daughter of Hortense McDuck and Quackmore Duck. According to comics writer Don Rosa, Della was "born" around 1920. Her twin brother is Donald Duck she is also the mother of Huey, Dewey and Louie Duck.
The identity of the boys' father is something of a mystery, as he is hidden by a bird and several branches on Disney comics artist Don Rosa's family tree. Very little is known about him. It was revealed in an early comic strip that Mr. Duck was sent to the hospital because Huey, Dewey and Louie placed a firecracker under his armchair as a prank, with disastrous results. It was because of this incident that Della (or "Dumbella" as she was called in the theatrical cartoon that introduced the nephews) sent her sons to her brother, Donald Duck. While originally meant to be a one-month stay, the nephews wound up staying with Donald permanently; the reasons for this are unknown. However, both she and Donald are linked to Scrooge McDuck in equal measure, and yet Donald is always referred to as Scrooge's closest living relative, suggesting she has disappeared or died.