A girl's not finished, unfortunately (4)
I believe the answer is:
alas
'unfortunately' is the definition.
('alas' is used to express regret)
'a girl's not finished' is the wordplay.
'girl' becomes 'lass' (lass can informally mean a girl).
'not finished' means to remove the last letter.
'lass' with its final letter taken away is 'las'.
'a'+'las'='ALAS'
(Other definitions for alas that I've seen before include "Exclamation of grief" , "Cry of grief" , "'- Poor Yorick' (Hamlet)" , "Woeful expression" , "Cry of regret" .)