Mrs. Fainall's role in The Way of the World is essentially that of a dual foil. On one hand, she is a foil to Fainall himself, her husband who neglects her and seems to have tired of her rapidly. On the other, she is a foil to Mrs. Marwood, her ostensible friend and genuine rival, with whom the initial dialogue that establishes her character and preoccupations takes place. With Mrs. Marwood, she discusses her hatred of men in general and her husband in particular.

Mrs. Fainall is a flat character in a play where verisimilitude is not of great importance, even for the protagonists. It is certainly plausible that any woman married to Fainall would quickly acquire a jaded view of men in general, and that she would be inclined to indulge in plots and intrigues. To this extent, the conduct of Mrs. Fainall is perfectly understandable and realistic. However, there is no attempt to add any depth to her character or any complexity to her motives. Even when she is not functioning as a foil, or driving the plot forward, Mrs. Fainall is principally defined by her relationship to others: Fainall's wife, Lady Wishfort's daughter, Mirabell's former lover, Mrs. Marwood's rival. It is her place close to the center of this tangle of relationships, rather than any personal quality she might possess, that gives Mrs. Fainall her importance in the drama.