Unattached girl with naughty secret (8)
I believe the answer is:
discrete
'unattached' is the definition.
(thesaurus)
'girl with naughty secret' is the wordplay.
'girl' becomes 'di' (**).
'with' is a charade indicator (letters next to each other).
'naughty' is an anagram indicator.
'secret' is an anagram of 'screte'.
'di'+'screte'='DISCRETE'
(Other definitions for discrete that I've seen before include "Individually distinct in discreet way" , "Individually separate and distinct" , "Unattached" , "Individual" , "independent" .)