Coffman was born on January 19, 1962 in Missouri. In 1986 she left her husband and child and took up with James Gregory Marlow, a career criminal she met through a prison correspondence, and the two travelled through the south-west committing robberies.
Between October and November 1986 they abducted and killed four women: Sandra Neary, thirty-two; Pamela Simmons, thirty-five; Corinna Novis, twenty; and Lynel Murray, nineteen. The women were taken from shopping centres and a dry cleaner's, raped, strangled, and left in vineyards and drainage ditches. They used the victims' bank cards.
They were arrested in November 1986. Coffman was convicted of the Novis and Murray murders and sentenced to death in San Bernardino County on August 31, 1989. The first woman to receive a death sentence in California since the penalty was reinstated in 1977. Marlow was also sentenced to death and died in prison in 2020.
Her defence at trial and on appeal has been that she was terrorised into participation by Marlow, who was violent to her throughout; the prosecution's case was that she was an active and willing participant, and evidence of her using the victims' cards and writing his name on her body was put to the jury. Both accounts are in the record.
She remains on California's death row, where no execution has been carried out since 2006 and a moratorium has been in force since 2019.