Maybe fire her over lunch? (6)
I believe the answer is:
heater
'maybe fire' is the definition.
'her over lunch?' is the wordplay.
'over' means one lot of letters goes inside another.
'lunch?' becomes 'eat' (to lunch can mean to eat lunch).
'her' enclosing 'eat' is 'HEATER'.
(Other definitions for heater that I've seen before include "Radiator" , "Warming device" , "fire" , "Source of warmth; gun" , "Room warmer" .)