Hallie's twin in "The Parent Trap" (5)
I believe the answer is:
annie
(Other definitions for annie that I've seen before include "Inane (anag) - girl (with a gun?)" , "Little orphan girl" , "Sharpshooter Oakley or musical orphan" , "Little Ophan .....; also a musical" , "-- Laurie, Scots song" .)