Mary Ann grew up in Durham county, northeastern England. According to some sources, she left home at age 16 to work as a nurse but returned three years later and became a dressmaker. In 1852 she married William Mowbray, and over the next decade or so, the couple had eight or nine children. (The lack of documentation such as birth and death certificates leaves many details of Mary Ann’s life open to dispute.) After moving frequently, the family settled in Hendon, Durham county, in about 1856. At some point William took out a life insurance policy that covered both him and their three surviving children; the others had died from “gastric fever,” a common ailment that had symptoms similar to arsenic poisoning. Gastric fever also claimed William’s life in 1864 and the lives of two other children soon afterward. Mary Ann received the insurance money, and she then left her daughter in the care of her mother.