Wrong about a girl (6)
I believe the answer is:
remiss
'wrong' is the definition.
(I've seen this before)
'about a girl' is the wordplay.
'about' becomes 're' (regarding).
'a girl' becomes 'miss' (term of address for an unmarried woman).
're'+'miss'='REMISS'
(Other definitions for remiss that I've seen before include "Failing in one's duty" , "Not taking care" , "At fault" , "Negligent, lax" , "Negligent in performance of duty" .)