Girl appearing on stage is not a true member (3,3)
I believe the answer is:
peg leg
'not a true member' is the definition.
I can't tell whether this defines the answer.
'girl appearing on stage' is the wordplay.
'girl' becomes 'peg' ().
'appearing on' is a charade indicator (letters next to each other).
'stage' becomes 'leg' (a leg is a stage of a competition).
'peg'+'leg'='PEG-LEG'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for peg leg that I've seen before include "Artificial limb (informal)" , "that supported Ahab" , "Artificial limb (usually of wood)" , "Silver piece's replacement" , "Person with a wooden limb" .)