Judith this may save you searching at NLA.
Mary Ann is listed as a passenger aboard the THERESA, arrived Victoria, October 1863 from London via Southampton.She is described as passenger number 270, from London, aged 24 years single, Church of England, housemaid, reads and writes, and was engaged to work at the Parsonage in Richmond for 3 years.
She was 1 year in 1841 census when she was with her grandparents, Daniel and Leah KNIGHTS and family at Barham Broom, Norfolk.
If this is her birth then would only be one year of age in Jun 1841.
Births Dec 1839
THURSTON Mary Ann Bethnal Green 2/4
I think Mary Ann's mother died in Jun qtr 1867 and her father married another Mary Ann [possibly CASEY] the same year.
The 1871 census lists Charles wife, Mary Ann as 42 years born Middlesex, City ie born c1829. Mary Ann KNIGHTS was born c1819 Barham Brook, Norfolk.
I'll type it all up tomorrow as bit late for me. If you don't want the info or you can access it yourself just say so.
Cando