Absent-minded girl's distinguishing feature (8)
I believe the answer is:
distrait
'absent-minded' is the definition.
(I've seen this before)
'girl's distinguishing feature' is the wordplay.
'girl' becomes 'dis' (I've seen this in other clues).
'distinguishing feature' becomes 'trait' (I've seen this before).
'dis'+'trait'='DISTRAIT'
(Other definitions for distrait that I've seen before include "Unable to concentrate for anxiety - it is trad (anag)" , "Preoccupied" , "Being one [SCATTY]" , "Inattentive or absent-minded, from French" , "Distraught in France" .)