Grandma set to retire somewhere in NW France (6)
I believe the answer is:
nantes
'somewhere in nw france' is the definition.
(French city)
'grandma set to retire' is the wordplay.
'grandma' becomes 'nan' (I've seen this before).
'set to' becomes 'set' ('set' can be a synonym of 'set to').
'retire' is a reversal indicator.
'set' in reverse letter order is 'tes'.
'nan'+'tes'='NANTES'
(Other definitions for nantes that I've seen before include "French FC" , "Loire city; its tolerant Edict" , "port abroad" , "French Atlantic port" , "City on the Loire, associated with 1598 edict ending the French Wars of Religion" .)