Aimless sort of girl (7)
I believe the answer is:
melissa
'girl' is the definition.
'aimless sort' is the wordplay.
'sort' indicates anagramming the letters.
'aimless' is an anagram of 'MELISSA'.
'of' is the link.
(Other definitions for melissa that I've seen before include "woman" , "Girl's name meaning "bee"" , "Female" .)