Maria plays a small but important part in the novel. She is Steppenwolf's mistress. This in itself is surprising — to readers, as well as to Steppenwolf — due to the age difference between them. Steppenwolf is a man in his fifties, while Maria is young woman, presumably in her twenties. Her principle purpose is to teach Steppenwolf about physical gratification and sexual pleasure — two concepts that he has considered primal, wolf-like, and vacuous.
It is important to note that even though Maria and Steppenwolf engage in conversation as well as sex, their relationship is defined by Hermine. Hermine arranges the affair, determines when it will begin by giving Maria Steppenwolf's key, and decides when it will end. Hermine tells Steppenwolf that "it's a poor fellow who can't take his pleasure without asking other people's permission." Hermine's task is to expose Steppenwolf to a hedonistic lifestyle, thereby revealing some of his other selves.
In a sense, Maria's role is one of preparation. She gives Steppenwolf his first taste of casual sex, unfettered, irresponsible, and lacking consequences. This is something that he has never experienced because he has always viewed sex through the lens of the bourgeoisie. Prior to this, sex was primarily a procreative act, within the traditional bounds of marriage.
Hermine describes Maria as "just the girl you need, Steppenwolf — pretty, young, light hearted, an expert in love and not to be had every day. If you hadn't to share her with others, if she weren't always merely a fleeting guest, it would be another matter." What Hermine is really saying is that Steppenwolf cannot be too serious about the affair, he cannot try to monopolize Maria, nor can he convince himself that it is love due to the temporal nature of their meetings. Once again, Hermine is responsible. She is not only teaching Steppenwolf about spontaneity and pleasure, but she is forcing him to not take things too seriously. In other words, Hermine is emphasizing what Goethe has already said, and what Mozart will repeat later.