Resident in Cymru since 2002, Marni was born in at the Presidio in San Francisco, California in the summer of 1956, and raised in Buffalo, New York. Her work has appeared in the UK, Canada, Australia, and the US. Her first novel, Knucklebones, was published by PS Publishing, the UK's premier genre publisher. She is married to Kevin and Wicked Stepmother to one stepson. In 2018 she founded Poems from the Doghouse to raise funds for her local animal shelter.