|Portrayed by Claire Jacobs|
|Significant Others:||Trevor Mathis † (husband)|
|Children:|| Colleen Mathis † (daughter)|
Aiden Mathis † (son)
Harriet's husband Trevor was the baggage handler for Flight 197. Her daughter Colleen went missing and Harriet assumed she had ran away from home. In actuality, she was kidnapped by the terrorist group Americon Initiative to use as leverage over Trevor, who unknowingly loaded the bomb on Flight 197. Not too long after the plane exploded, Aiden found Trevor dead in his workshop. It looked like Trevor had committed suicide, but he had been murdered by Pascal LeMarchal. After Aiden left home, Harriet was left alone. Years later, Aiden would learn the truth about Colleen's disappearance, but he didn't tell Harriet the truth because she thought Colleen was alive and happy and he didn't want to upset her with the truth.
- With the death of Aiden, Harriet is the last known living member of the Mathis Family.
- It is currently unknown if Harriet is aware of Aiden's death.