Her birth year of 1814 (or 1813) is consistently reported in all censuses, as is the birth place of Dunton, Bucks where her father was rector from 1811 to 1817, when he was appointed chaplain to the bishop of London.

Then I found this transcription of the baptism register for St Martin’s church, Dunton:

24 Mar 1814   Maria daughter of Charles James & Anna Maria BLOMFIELD of Dunton, Clerk, Rector of Dunton
___________________

In 1881 she was a widow in the census:

Name  Relation  Condition  Sex  Age  Birth Year  Occupation  Disability  Where Born

BROWN, Maria Head Widow F 67 1814   Dunton, Buckinghamshire
BROWN, Alice M Daughter Single F 36 1845  Shornecliffe, Sussex
BROWN, Charles J Son Single M 22 1859 Insurance Clerk  Woolwich, Kent
MACLEAN, Emma Servant Married F 42 1839 Cook (Dom)   Wellington, Somerset
WEBB, Rosina Servant Single F 20 1861 Parlour Maid (Dom)  Greenwich, Kent
CLARK, Alice Servant Single F 14 1867 Housemaid (Dom)   Rotherhithe, Surrey

RG number: RG11 Piece: 740   Folio: 138 Page: 21    

Registration District: Woolwich Sub District: Charlton
EnumerationDistrict: Ecclesiastical Parish:

Civil Parish: Charlton Next Woolwich   Municipal Borough:
Address: Hemblington Ho, Fairfield Row, Charlton Next Woolwich
_________________________________________


There are far too many Maria Brown deaths on FreeBMD to begin to guess her death date.

2009: She was in the 1881 census as a widow but not in 1891, so a search for those ten years for her death gives:

Surname First name(s) Age District Vol  Page

Deaths Sep 1881   (>99%)
BROWN Maria 67 Coventry 6d 263
Deaths Mar 1882   (>99%)
BROWN Maria 67 Derby 7b 326
Deaths Jun 1883   (>99%)
BROWN Maria 70 Norwich 4b 97
BROWN Maria 69 Birmingham 6d 114
BROWN Maria [5_]2 Wokingham 2c 259
Deaths Mar 1884   (>99%)
Brown Maria 69 Woolwich 1d 699      <------
Brown Maria 71 Kensington 1a 59
Deaths Jun 1884   (>99%)
Brown Maria 70 Goole 9c 413   
Deaths Dec 1885   (>99%)
BROWN Maria 71 Leeds 9b 304   
BROWN Maria 71 Guisbro' 9d 301   
Deaths Mar 1886   (>99%)
Brown Maria 73 Poplar 1c 510   
Deaths Mar 1887   (>99%)
Brown Maria 8[14] Yarmouth 4b 17   
Deaths Jun 1887   (>99%)
Brown Maria 72 Islington 1b 127   
Deaths Sep 1887   (>99%)
Brown Maria 73 Edmonton 3a 156   
Deaths Mar 1888   (99%)
BROWN Marianne 73 Cambridge 3b 357   
Deaths Mar 1890   (>99%)
BROWN Maria 75 Horsham 2b 240   
BROWN Maria 76 Shoreditch 1c 82   
Deaths Mar 1891   (>99%)
Brown Maria 76 Wellingbro 3b 113

I have highlighted in red the obvious candidate, for age and location.

So this looks very much as if it is her death:

Surname   Given Name   District   Volume  Page
Deaths Mar 1884
Brown Maria Woolwich 1d 699
_________________

Their marriage:

Name Maria Blomfield
District      Kensington, Middlesex
Spouse Henry Brown
Page 0208
Volume 3
Registered October - December 1843
_________________

The Vlieland family researchers have obtained these details of the marriage:

> THE GENTLEMAN'S MAGAZINE  By SYLVANUS URBAN, GENT. Vol 21 MDCCCXLIV
> January to June (1844) 1843 - Nov 2: At Fulham, the Rev. Henry Brown,
> M.A., Incumbent of St. James's, Curtain-road, to Maria, eldest dau. of
> the Lord Bishop of London.
>
> The Ecclesiastical Gazette, or, Monthly register of the affairs of the
> Church of England – From July 1842 to June 1843 MARRIAGES: Rev. Henry
> Brown, Perpetual Curate of St. James's, Curtain road, Shoreditch,
> London, to Maria, eldest daughter of the Right Hon. and Right Rev. the
> Lord Bishop of London.  (no date shown) - these first two are on
> Google Books
>
> Saturday 11 November 1843 Yorkshire Gazette (also syndicated) - On
> Thursday, the 2nd inst. .....at the parish church of All Saints,
> Fulham, by the Rev. R. G. Baker, the Rev. Henry Brown, M.A., of
> Balliol College, Oxford, and Incumbent of St. James's, Curtain-road,
> to Maria, eldest daughter of the Right Hon. and Rev. the Lord Bishop
> of London.
_________________