In addition to the glass menagerie, especially the glass unicorn, symbolizing Laura's fragility and feelings of freakishness, the glass further symbolizes her hidden inner radiance. Her inner radiance is symbolized through the glass's ability to radiate light, as she points out to Jim when she hands him the unicorn: "Hold him over the light, he loves the light! You see how the light shines through him?" (Scene VII). Little does she realize that she equally emits light due to her gentleness, goodness, and prettiness. The loss of the unicorn's horn further symbolizes Laura shedding her belief that she is "freakish," a belief Jim helps her shed by commenting that he never noticed her brace and that he wished she had made more friends, and by conversing with her, dancing with her, calling her pretty, and kissing her.
Yet, one may argue against the interpretation that Laura giving him the broken unicorn after he announces he is engaged means that she is relinquishing her understanding that she isn't freakish or of giving Jim the new feelings of normalcy he has inspired in her. Instead, one might argue that it symbolizes that, despite the discouraging news, she now knows that she no longer needs to seek refuge in her menagerie, especially not in a figurine that she thinks represents her freakishness. Jim has not only made her realize that her perceptions of herself are all wrong, but also that she is actually very special--these are not revelations one can easily shrink from once gained.
One can reach a more positive interpretation of her giving Jim the broken unicorn when one takes a more careful look at the final stage directions. Though Tom abandons his mother and sister, the stage directions indicate that, though Laura's hair is covering her face during Tom's final speech, at the very end of his speech, Laura "lifts [her face] to smile at her mother." The smile is not indicative of a completely tragic ending for Laura. Instead, it indicates that, by the end of the play, both Laura and her mother have learned to let go of their past torments and embrace a future in which they can survive on their own, without Tom, who only served as a crutch preventing them from fully healing because they relied on him so much for their survival.