Wasted, girl locked up (8)
I believe the answer is:
misspent
'wasted' is the definition.
(I've seen this in another clue)
'girl locked up' is the wordplay.
'girl' becomes 'miss' (term of address for an unmarried woman).
'locked up' becomes 'pent' (I've seen this in other clues).
'miss'+'pent'='MISSPENT'
(Other definitions for misspent that I've seen before include "Wasted (as youth)" , "Squandered" , "Like many a youth" , "Passed the time unwisely, as a youth perhaps" , "wasted away?" .)