Theresa Duncan was born in Michigan to William R. Duncan and Janet (née Cardelli) Duncan. Specific details about her early childhood location are not widely available.

Theresa experienced a Catholic school education. Details about her specific schools and elementary education are scant, but this period cultivated her interest in religion, mythology, and visual storytelling. These themes would become recurring motifs in her later work.

Duncan attended Marian High School in Bloomfield Hills, Michigan, an all-girls Catholic school. There, she displayed an early aptitude for creative expression and began developing her unique artistic sensibility. Specifics regarding her academic achievements and extracurricular activities during this period are less documented.