Girl to form an attachment with? (3)

I believe the answer is:

peg

I'm a little stuck... Click here to teach me more about this clue!

'girl' is the definition.

I don't understand the remainder of the clue.

(Other definitions for peg that I've seen before include "Fix (a price)" , "Clip for hanging washing" , "Brandy and soda drink measure" , "Projecting pin" , "Member" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app