In Shaw's play it is the character of Ann Whitefield who encourages and cajoles John Tanner—the would-be superman of the title—to become "that which he is," to paraphrase the subtitle of one of Nietzsche's books. She is the animating spirit of the action, the life-force which incites Tanner to develop into something more substantial than the unthinking anarchist, the impetuous, hot-headed would-be revolutionary.
In doing so, Ann takes on the role of a female Don Juan, cleverly seducing Tanner into an arrangement with which he feels rather uncomfortable, largely on account of his disdain for the niceties of bourgeois social convention. Ann's vigorous assertion of her individuality presents a model for Tanner to emulate. In Nietzschean terms this isn't so much a creative evolution of personality as a rediscovery of what's truly inside. The greatest spirits of every age have superman within them, both men and women.