Marie Laustin serves as matriarch of the affluent Parisian bourgeois Laustin family. Married to Léon Laustin, she occupies the role of a stay-at-home wife, consistently aligning with her husband’s viewpoints and decisions without notable opposition. Her character upholds conventional class values, emphasizing exclusivity in her daughters' social circles within the bourgeoisie and adherence to traditional decorum.

She displays overt favoritism toward eldest daughter Geneviève, celebrating her grace, elegance, and musical talents as the family’s crowning achievement. This contrasts sharply with her reserved dynamic toward younger daughter Isabelle, whose childhood rebelliousness and tomboy inclinations provoked concern, though Marie held hope for Isabelle’s eventual embrace of ladylike conduct.

Marie’s compliance with patriarchal and class norms surfaces during familial discord. When Geneviève rejects an arranged engagement to Captain Victor Langlois for Jules Francoeur, a lower-class piano teacher, Marie reacts with visible anguish and tears. Despite this distress, she refrains from intervening as Léon disowns Geneviève and expels her from their home.

The Franco-Prussian War’s outbreak and the family’s relocation to Versailles unveil deeper fractures. During a confrontation involving their son Andréa—presumed dead in battle but later revealed alive—Marie is physically restrained by him. This immobilization inadvertently causes her death when a falling chandelier strikes her.

Léon attributes Marie’s demise to Count Red, a charge stemming from misinformation. This false accusation results in sparse attendance at their joint funeral, reflecting their fractured social standing even posthumously.