She sounds a duck (3)
I believe the answer is:
ida
'she' is the definition.
(I've seen this before)
'sounds a duck' is the wordplay.
'sounds' shows a homophone (sound like).
'a duck' becomes 'eider' (eider is a type of duck).
'eider' sounds like 'IDA'.
(Other definitions for ida that I've seen before include "Girl's name; aid (anag.)" , "Industry development group" , "Stagey princess" , "Greek mount - Gilbertian princess" , "Poetic princess" .)