Musical heroine joining Laurie in a song (5)
I believe the answer is:
annie
This might be a double definition.
'musical heroine' is the first definition.
(I've seen this before)
'laurie in a song' is the second definition.
'annie' can be an answer for 'laurie' (I've seen this in another clue). I am not certain of the 'in a song' bit.
'joining' acts as a link.
I am not very happy about this link. It may belong to one of the definitions.
(Other definitions for annie that I've seen before include "Little Ophan .....; also a musical" , "Famous musical about orphan girl" , "-- Oakley (Wild West)" , "Miss Laurie" , "Musical about markswoman" .)