Madame Forestier is a dear friend of Mathilde's and a symbol of luxury and decadence. She embodies everything that Mathilde envies and longs for, but has never been able to obtain due to her modest upbringing. Rather than allowing her wealth to launch her into a life of greed and materialism, Madame Forestier remains kind and generous. When Mathilde approaches her to borrow jewels for the ball at the Ministry, Madame Forestier graciously agrees and allows Mathilde to choose whichever pieces she desires.
Madame Forestier's surprising revelation that the diamond necklace is a fake offers a compelling commentary on the contrast between the two women. Mathilde allows her desire for wealth and status to uproot her life. Even before the incident with the lost necklace, the narrator explains that Mathilde had begun to distance herself from Madame Forestier. She chooses to pull away from her kind-hearted friend to avoid confronting her own meager lifestyle in comparison to Madame Forestier’s luxurious one. Unlike Mathilde, Madame Forestier does not infuse material objects with excessive value. Though wealthy, she understands that possessions should not dominate one’s life. She casually shares her belongings with Mathilde and even purchases fake jewels for her collection.
When Mathilde confesses that she lost the original necklace, Madame Forestier is more concerned with the wasted years of Mathilde's life than the necklace itself. Evidently, Madame Forestier grasps a fundamental truth that Mathilde is unable to discern—that material objects only hold power if we give them that power. Choosing to purchase a fake diamond necklace instead of a real one, despite likely being able to afford it, indicates that Madame Forestier understands that true value is derived from perception. Her role in the story therefore juxtaposes Mathilde's shallow, materialistic approach to life, her very existence defined by an obsession with status and appearances.