Wrong to free her for this reason (9)
I believe the answer is:
therefore
'for this reason' is the definition.
(I've seen this before)
'wrong to free her' is the wordplay.
'wrong' is an anagram indicator.
'to'+'free'+'her'='tofreeher'
'tofreeher' with letters rearranged gives 'THEREFORE'.
(Other definitions for therefore that I've seen before include "It follows" , "Thus" , "as result" , "has a triangular formation in maths?" , "In consequence" .)