Agamemnon's daughter (7)
I believe the answer is:
electra
'agamemnon's daughter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for electra that I've seen before include "type of complex" , "heroine of Greece" , "Greek heroine (with a complex!)" , "Daughter of Agamemnon and Clytemnestra (who has a complex?)" , "King's daughter" .)