Anne-Marie is Cecil's biological granddaughter who has cared for Sebastian since infancy within their adoptive family. Approximately eleven years older than Sebastian, she functions as an older sister yet frequently adopts a maternal self-perception due to her integral role in his upbringing alongside Cecil.

Her personality blends deep affection with overprotectiveness, occasionally expressed through harshness—such as locking Sebastian in the stables as punishment for childhood wanderings. She reacts strongly to Sebastian's longing for his biological mother, interpreting it as rejection of her caregiving, with visible frustration escalating in early episodes.

Physically depicted with red hair and a matching temperament, she approaches household duties with intense seriousness, directing Sebastian firmly on chores. Her romantic relationship with Dr. Guillaume, the village doctor, evolves over time. This courtship culminates in her receiving a wedding dress crafted by Isabel, Sebastian's biological mother, signaling impending marriage. Isabel's creation of the dress subtly bridges the maternal figures in Sebastian's life.

Throughout the series, she remains a consistent disciplinarian and devoted family member within the rural French mountain setting. Her evolution transitions her from a sibling-like caregiver to an adult navigating marriage while confronting complexities in Sebastian's search for his origins.