Expression in Green Finch and Linnet Bird? Sweeney Todd?

I am currently playing the role of Johanna in a production of Sweeney Todd. Opening Night is this Friday, and I am doing quite well with the song "Green Finch and Linnet Bird," according to the directors, however, they told me that although the song sounds pretty, I am having trouble expressing enough emotion during the song. I portrayed her as sad and longing, because I know this is the "I Want" song of the show. I understand that the bird is symbolic of Johannas situation. Any direction or suggestions as to how to show expression at certain parts of the song would be greatly appreciated. Thank You! :)