Heroine, tragic victim of hubris? Old enough to see through this (6)

I believe the answer is:

isolde

I'm a little stuck... Click here to teach me more about this clue!

'heroine' is the definition.
(I've seen this before)

'tragic victim of hubris? old enough to see through this' is the wordplay.
'ISOLDE' is hidden within the letters.
But, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for isolde that I've seen before include "Lover of Tristan" , "Arthurian queen" , "King Mark's betrothed (Wagner)" , "princess of legend" , "Tristram's lover, quite soiled" .)

I've seen this clue in The Guardian.

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