Blanche again mentions Shep Huntleigh. He, too, has taken on a symbolic meaning for Blanche. What does he represent to her? Why does she tell Stanley a lie about Shep Huntleigh?

Shep represents everything that Blanche wants and cannot have. Shep Huntleigh is an illusion, he doesn't exist except in her mind. Blanche lies because that's what she does, her reality isn't desirable. Thus, she makes it what she wants by lying.