I don’t think this is her birth (wrong second name, wrong county):

Surname First name(s) District Vol Page
Births Sep 1867   (>99%)
Curzon Mary Agnes Stoke T. 6b 183

Nothing like her in the 1871 census.

In 1881 she was aged 14 and with her mother in North Camp, Farnborough.
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Possible marriages:

Surname First name(s) District Vol Page
Marriages Dec 1882   (>99%)
CURZON Mary Ellen Belper 7b 1038   
Marriages Jun 1888   (>99%)
Curzon Mary Ellen Marylebone 1a 946   
Marriages Mar 1897   (>99%)
Curzon Mary Elizabeth Shardlow 7b 607   
Marriages Sep 1900   (>99%)
Curzon Mary Ellen Derby 7b 974   
Marriages Jun 1901   (>99%)
Curzon Mary Elizabeth Chesterfield 7b 1506   
Marriages Sep 1906   (>99%)
CURZON Mary Elizabeth Derby 7b 1169   
Marriages Jun 1907   (>99%)
CURZON Mary Elizabeth Leicester 7a 489   
Marriages Sep 1907   (>99%)
CURZON Mary Emma Chesterfield 7b 1457   

Surname First name(s) Spouse District Vol Page
Marriages Mar 1913   (>99%)
Curzon Mary E Dodwell Northwich 8a 433   
Marriages Jun 1914   (>99%)
Curzon Mary E Curzon Northwich 8a 610
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The marriage in 1888 is particularly tempting:

Surname First name(s) District Vol Page
Marriages Jun 1888   (>99%)
Burrell Sarah Elizabeth Marylebone 1a 946   
Curzon Mary Ellen Marylebone 1a 946   
ISAACS Fred Walter Marylebone 1a 946   
ISAACS Frederick Walter Marylebone 1a 946   
WHITFELD Arthur Lewis Marylebone 1a 946
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A possible entry for her in 1891 as this is the only Mary E in the above marriage list who is also born in Leics.:

Name Relation Condition Sex Age Birth Year Occupation  Disability  Where Born

WHITFELD, Arthur L Head Married M 28 1863 Clerk In Holy Orders
Lewes, Sussex
WHITFELD, Mary E Wife Married F 25 1866   Twycross, Leicestershire
WHITFELD, Arthur N Son M 0 (4M) 1891   Bradenham, Buckinghamshire
GRIMSHAW, Harry Servant M 14 1877 Page Domestic Servant  Reading, Berkshire
MARTIN, Mary A Servant Single F 26 1865 Cook Domestic Servant  Leighton, Somersetshire
LEGG, Ellen J Servant Single F 30 1861 Nurse Domestic Servant  Nettlecombe, Dorsetshire

RG number: RG12 Piece: 1141 Folio: 74 Page: 1    

Registration District: Wycombe Sub District: West Wycombe
EnumerationDistrict: 7 Ecclesiastical Parish: St Botolph

Civil Parish: Bradenham Municipal Borough:
Address: The Rectory, Village, Bradenham
County: Buckinghamshire
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And in 1901 there were two more sons (but where was Arthur N?):

Name Relation Condition Sex Age Birth Year Occupation  Disability  Where Born

WHITFELD, Arthur L W Head Married M 38 1863 Clergyman Ch Of England
Lewes, Sussex
WHITFELD, Mary E Wife Married F 35 1866   Twycross, Leicestershire
WHITFELD, Ernest H Son Single M 6 1895   Lt Easton, Essex
WHITFELD, Gerald H P Son Single M 5 1896   Lt Easton, Essex
GREEN, Margaret E Servant Single F 30 1871 Cook Domestic  Roude, Northamptonshire
GREEN, Gertrude Servant Single F 31 1870 H P M Domestic  Earls Colne, Essex
GARDNER, Eliza Servant Single F 20 1881 Nurse Domestic  Berkeley, Gloucestershire

RG number: RG13 Piece: 1729 Folio: 79 Page: 6    

Registration District: Dunmow Sub District: Stebbing EnumerationDistrict: 7
Ecclesiastical Parish: Little Easton

Civil Parish: Little Easton Municipal Borough:
Address: The Rectory, Little Easton
County: Essex
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Finally in 1911, Arthur N reappears, apparently married - but not when the form is cursorily examined!.  Mary says she has had 3 children, all of whom are living. This time Mary’s birth is given as Gopsall, Leics, to me confirming that she is indeed the grand-daughter of the 1st earl whose country pad was at Gopsall Hall, Norton, Leics:

Name Relation Condition/ Yrs married Sex Age Birth Year Occupation  Where Born

WHITFELD, Arthur Lewis Head Married
23 years M 48 1863 Clerk In Holy Orders E C Lewes Sussex
WHITFELD, Mary Ellen Wife Married 23 years F 45 1866  Gopsall, Leicestershire
WHITFELD, Arthur Noel Son Married M 20 1891 Army : 2nd Lieut: Bradenham, Bucks
SMITH, Elizadbeth Ann Servant Single F 60 1851 Domestic Service Cook  Langford, Budfield, Somerset
BREWER, Edith Mary Servant Single F 23 1888 Domestic Service H P M  Birch, Essex

RG number: RG14 Piece: 7883
Reference: RG14PN7883 RG78PN393 RD145 SD1 ED20 SN136

Registration District: Wycombe Sub District: Wycombe EnumerationDistrict: 20
Parish: Hughenden

Address: Whitfeld Hughenden Vicarage High Wycombe
County: Buckinghamshire
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Burke’s Peerage confirms all the above.

Their marriage:

Surname First name(s) District Vol Page
Marriages Jun 1888   (>99%)
Curzon Mary Ellen Marylebone 1a 946   
WHITFELD Arthur Lewis Marylebone 1a 946