"Giant" author Ferber (3)
'giant author ferber' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for edna that I've seen before include "Prolific Irish woman novelist . . . . O'Brien" , ". . . . O'Brien, ... Saint Vincent Millay" , "Dean (anag) - it's a girl's name!" , "Barry Humphries' Dame" , "Girl for Dane" .)
(Other definitions for dna that I've seen before include "Main constituent of chromosomes" , "Initially, it stores genetic information" , "Briefly, substance in chromosomes used by police to identify criminals" , "Substance that stores genetic information - often used by police" , "Substance that stores genetic information in body" .)