Wagnerian heroine in the Valkyries? Yes and no (3)
I believe the answer is:
eva
'wagnerian heroine' is the definition.
(character in Die Meistersinger von Nrnberg)
'the valkyries? yes and no' is the wordplay.
'EVA' is hidden within the letters.
However, I am uncertain how the hidden word is indicated.
'in' is the link.
(Other definitions for eva that I've seen before include "- Braun, Hitler's mistress" , "Miss Peron, perhaps" , "-- Braun, Hitler's wife" , "Woman" , "Braun, Brick or Peron" .)