Girl retains a right to pillage (6)
I believe the answer is:
maraud
'to pillage' is the definition.
(I've seen this in another clue)
'girl retains a right' is the wordplay.
'girl' becomes 'maud' ().
'retains' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'a'+'r'='ar'
'maud' going around 'ar' is 'MARAUD'.
(Other definitions for maraud that I've seen before include "Harry" , "Wander in search of plunder" , "Rove around raiding" , "Sack" , "Raid and rove in search of booty" .)