Big gun criminal girl brought in (6)
I believe the answer is:
cannon
'big gun' is the definition.
(I've seen this before)
'criminal girl brought in' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'girl' becomes 'ann' (woman's name).
'brought in' means one lot of letters goes inside another.
'con' going around 'ann' is 'CANNON'.
(Other definitions for cannon that I've seen before include "Field gun" , "One of the big guns" , "Heavy artillery piece" , "Weapon firing large balls" , "Large artillery piece" .)