More information:

1900 census in New Orleans at 2709 Rampart Street:

Mary Nelson, born December 1839, widowed, born in Ireland
Joseph Nelson, born October 1874, son, father born in Denmark (occupation: Sheet iron laborer)

Mary is listed as the mother of 7 children, 6 still living
She immigrated to the US in 1840. She was married 36 years.