[3] On 18 April 1808, she married Davies Giddy, a Cornish landowner, who had served as High Sheriff of the Duchy.

Mary Ann Gilbert was passionately concerned about low agricultural productivity and the plight of the rural poor.

[citation needed] Sharing her husband's interest, Mary Ann Gilbert managed some successful practical agronomical experiments at Beachy Head in feeding the poor, or rather, teaching them to feed themselves using land no one else wanted, for a fair rent.

Among those who advised her were Richard Whately, Anglican Archbishop of Dublin and his brother, the Vicar of Cookham in Berkshire, Edwin Chadwick and William Gill, of Chacewater, Cornwall.

Her illustrations appear in Thomas Bond's Topographical and historical sketches of the boroughs of East and West Looe, in the county of Cornwall (1823).