Isabelle Mueller is the wife of Lewis Mueller, a former aerial stunt pilot left permanently disabled when his plane was sabotaged by Sam Ibrahim during a race. She has long brown hair, brown eyes, and a distinctive mole under her left eye. Her typical attire features a sleeveless laguna yellow dress, a white belt, a necklace, gold earrings, and white high-heel shoes, often paired with red lipstick.

Isabelle displays a calm and soft-spoken demeanor, contrasting her husband. She is a capable actress who uses this skill to aid Laurent Thierry's confidence schemes. After Lewis's accident, she serves as his primary caregiver, managing his daily needs due to his wheelchair-bound condition.

Her backstory revolves around her marriage and the plane crash's aftermath. She harbors deep resentment toward Sam Ibrahim, blaming him for Lewis's paralysis, which drives her involvement with Laurent's team in the "Singapore Sky" arc. When Laurent recruits Lewis for a con against the Ibrahim brothers, Lewis declines on moral grounds but permits Isabelle to assist if she chooses. She independently decides to participate, leveraging her acting abilities to execute the plan.

In the con, Isabelle poses as an intermediary to introduce Makoto Edamura to Clark Ibrahim as a new mechanic. Her convincing performance demonstrates her commitment to the scheme and her desire for retribution against Sam, underscoring her agency and dedication to avenging her husband.

She undergoes no significant development or appearances beyond the "Singapore Sky" arc, with her portrayal centered on her relationship with Lewis, her resentment toward Sam, and her calculated participation in the con.