Elsa's Frozen sister (4)
I believe the answer is:
anna
'elsa's frozen sister' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for anna that I've seen before include "Palindromic girl's name" , "- - Kournikova (tennis)" , "Unit of length" , "Miss Karenina" , "-- Karenina, Tolstoy novel" .)