Girl with an American lawyer (3)
I believe the answer is:
ada
'girl' is the definition.
(girl's name)
'with an american lawyer' is the wordplay.
'with' is a charade indicator (letters next to each other).
'an' becomes 'a'.
'american lawyer' becomes 'DA' (abbreviation for 'District Attorney').
'a' put next to 'da' is 'ADA'.
(Other definitions for ada that I've seen before include "Computer lang.; f. name" , "Girl's name, one letter short of a man's name" , "-- Lovelace, pioneer in computing" , "Programming language" , "girl?" .)