She is on the 1939 register, of which I only have the free access:
Mercy Greenman 1849 Chippenham M.B. Wiltshire
There's an online tree that says she married John Greenman and that these were the children of the marriage: Albert Greenman, Edith Maud Greenman and Arthur John Greenman.
On the 1881 census
Greenway Lane, Chippenham
John Greenman 31 Kington St Michael, Wiltshire, England
Mercey Greenman 30 Cold Ashton, Gloucestershire, England
Arthur J Greenman 4 Chippenham, Wiltshire, England
Edith M Greenman 5 Box, Wiltshire, England
Kate Night Boarder 9 Chippenham (U S D), Wiltshire, England
Inft Unnamed Greenman 0 Chippenham, Wiltshire, England
Page Number 35
Registration Number RG11
Piece/Folio 2033/43
On the 1891census
Lowden, Chippenham
John Greenman 39 Wiltshire, England
Mercy Greenman 40 Gloucestershire, England
Edith M Greenman 15 Wiltshire, England
Arthur John Greenman 12 Wiltshire, England
Herbert Geo Greenman 7 Wiltshire, England
Ida May Greenman 5 Wiltshire, England
Frederick M Greenman 1 Wiltshire, England
Violet Greenman 0 Wiltshire, England
Page Number 29
Registration Number RG12
Piece/Folio 1594/ 18
On the 1901 Census
Malmesbury Rd, Chippenham
John Greenman 49 Kington St Michael, Wiltshire
Mercy Greenman 51 Cold Ashton, Gloucestershire
H G Greenman 17 Chippenham, Wiltshire
T M Greenman 15 Chippenham, Wiltshire
F M Greenman 11 Chippenham, Wiltshire
Gertrude V Greenman 10 Chippenham, Wiltshire
Frederick G G Walker Boarder 25 Grewelthorpe, Yorkshire
Henry C Ames Boarder Burnham, Somersetshire
Schedule Type 308
Page Number 43
Jamjar