Teresa was born in Van Nuys, California, 1949. Her family moved to northern California when she was a teenager, then back to southern California (briefly), and finally to the San Francisco Bay Area, where she has lived ever since.

Teresa She met her husband, John Edgerton, in 1971, at the local Renaissance Faire, where she was working as a Tarot reader and he was part of a Society for Creative Anachronism troupe putting on demonstrations of medieval tourney combat. They became better acquainted through their involvement in the SCA, and other historical recreations, and were married, in her parent's back yard in an early Tudor-style ceremony, a mere eight months later.

In 1973 they started their family, welcoming daughter Gwyneth Alianora, who missed being born on Halloween by less than two hours. Twenty months later, a second child, Daisy Elizabeth, was born. Often mistaken for twins, Gwyneth and Daisy spent much of their time growing up posing in a variety of Medieval, Renaissance, and Victorian costumes.

Meanwhile, Teresa, determined to remain a stay-at-home mother, spent the next several years attempting to add to the family income by working as a professional psychic and by making puppets. She, John, and the girls (now joined by Megan Angharad) barely scraped by. At the age of twenty-nine, Teresa decided that it was time to get serious about her life-long ambition to become a writer. She spent the next several years writing the steadily expanding epic that would eventually become The Green Lion Trilogy. The family was also expanding, with the birth of a fourth child, John-Miles (more of a surprise than an accident).

Child of Saturn was published in 1989. Two sequels soon followed. After that, Teresa's writing production slowed down somewhat, as the demands of motherhood, baseball (both Megan and Miles spent a number of years in Little League), and volunteer work at the local elementary school took up much of her time. There were also severe health problems, which slowed down the writing process even more, and led to a period of virtual seclusion.

Teresa, Gwyneth, and Daisy at the Dickens Faire Now, with her health restored, and having reached the venerable age of fifty, Teresa finds herself the grandmother of twins and the author of eleven books and six short stories—nine of those books published under her own name, and two under her pseudonym, Madeline Howard.

Her eleventh book, A Dark Sacrifice, was published in December 2007.