On 18 April 1808, she married
Davies Giddy, a
Cornish landowner, who had served as
High Sheriff of the Duchy. He was an M.P. for Cornish constituencies from 1806 to 1832. Among his roles in Parliament was as Chairman of the
Board of Agriculture. Mary Ann Gilbert was passionately concerned about low agricultural productivity and the plight of the rural poor. Davies was more interested in how the
Parish Rate for the support of unemployed might be reduced. In 1814, Mary Ann Gilbert's uncle, Charles Gilbert, died. In his will, he left her much property in
Sussex, or to a future husband, if he changed his name to "Gilbert". In December 1817 Davies Giddy took his wife's surname, "Gilbert", to perpetuate it. In January 1818, the names of their children were also changed. ==Agronomic experiment==