This looks like Mary with two of her children in 1841:
HO107; Piece 787; Book: 5; Civil Parish: Heigham; County: Norfolk; Enumeration District: 12; Folio: 11; Page: 14; Line: 5
http://search.ancestry.co.uk/iexec?h...=&pid=16014249
and in 1851 Mary is living with her eldest son, James:
HO107; Piece: 1811; Folio: 73; Page: 13
http://search.ancestry.co.uk/iexec?h...c=&pid=5106143
Mary Ann's birth is also on BMD registers under Horton:
Horton Mary Ann Father: William Horton 1809 Birth Norfolk RG6_1048