Fortunate girl about to finish work (5)
I believe the answer is:
lucky
'fortunate' is the definition.
(synonyms)
'girl about to finish work' is the wordplay.
'girl' becomes 'lucy' (girl's name).
'about' means one lot of letters goes inside another.
'to finish' suggests the final letters.
The last letter of 'work' is 'k'.
'lucy' placed around 'k' is 'LUCKY'.
(Other definitions for lucky that I've seen before include "Auspicious" , "'It is better to be born . . . . . than rich'" , "Fortunate" , "Bringing good fortune" , "Blessed with good fortune" .)