Undaunted, the girl's voice is without limits (6)
I believe the answer is:
heroic
'undaunted' is the definition.
(I've seen this before)
'the girl's voice is without limits' is the wordplay.
'the girl' becomes 'her' (I've seen this in another clue).
'is without limits' indicates the central letters (letters at the edges or 'limits' are removed).
The central letters of 'voice' are 'oic'.
'her'+'oic'='HEROIC'
(Other definitions for heroic that I've seen before include "Dramatic" , "Imposing or impressive: very courageous" , "Surpassing the ordinary, in courage say" , "Extravagant" , "Superhuman (efforts)" .)