Because her mother died in 1798 and her brother was born in 1796, she must have been born around 1797.  The 1851 census gives 1799 for her birth but she could still have been 52 and born in 1798, which is now the best guess.

In fact she was born in 1797, from her baptism:

First name(s)           Sarah
Last name               Charlewood
Birth year              1797
Birth date              19 Oct 1797
Baptism year            1797
Baptism date            28 Nov 1797
Baptism place           Checkley, St Mary & All Saints
Denomination            Anglican
Father's first name(s)  Chars Benn
Mother's first name(s)  Jane
County                  Staffordshire
Country                 England
Archive reference       D3955/1/3
Page                    18
Register type           Baptism & burial
Record set              Staffordshire baptisms
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She and Charles had issue, thought to be:
Sarah Amelia
George Edward
John James
Jane Sophia
Mary Catherine
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This looks very much like them in the 1851 census:

Name  Relation  Condition  Sex  Age  Birth Year  Occupation  Disability  Where Born

MARTIN, Charles W  Head     Married  M  52  1799  Landed Proprietor, Captain Mexican Navy
                                                  Retained E. India Service    Great Ness, Shropshire
MARTIN, Sarah      Wife     Married  F  52  1799  Wife Of Landed Proprietor    Chickley, Staffordshire
MARTIN, Charles W  Son       M  20  1831  East India Compy  Artillery  Broam, East Indies
MARTIN, Mary C     Daur       F  18  1833  Scholar                      Broam, East Indies
MARTIN, George E   Son               M  17  1834  Naval Cadet                  Broam, East Indies
John J    Martin   Son      -       M  12  1839  Scholar                      Pendleton, Lancashire
Mary      Vye      Servant  -       F  31  1820  Ladies Maid                  Christchurch, Hampshire
Susan     Barber   Servant  -       F  22  1829  Cook                         South Down, Hampshire
Ann       Caine    Servant  -        F  20  1831  Housemaid                    Christchurch, Hampshire

RG number: HO107 Piece: 1666 Folio: 416 Page: 7    
  
Registration District:  Lymington
Sub District:
Enumeration District:  
Ecclesiastical Parish: St Marks High Cliff
  
Civil Parish:             Milton
Municipal Borough:        
Address:                  Belvidere House Chewton, Milton
County:                   Hampshire
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In 1861 she was Head of the household, still Belvedere House in Chewton, Milton which was in the registration district of Lymington, probably widowed, and with her three daughters:

Mary C. b. 1833 in Broam (?), East Indies
Jane  S, b. 1835 in M? G??, Yorkshire
Emily L, b. 1836 in Manchester, Lancs
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In 1871 she had moved to Christchurch and had her daughter Emily with her.
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In 1881 Mary C was 48, born in Burvah (?) and living with a widow, Anne Turner some 13 years older than her.
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Her death in registration index:

First name(s)  SARAH
Last name      MARTIN
Gender         Female
Birth day      -
Birth month    -
Birth year     1797
Age            75
Death quarter  4
Death year     1872
District       LYMINGTON
County         Hampshire
Volume         2B
Page           367
Country        England
Record set     England & Wales deaths 1837-2007

Lymington district was adjacent to Christchurch.
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She had the following children:

George Edward Martin of 74 Westbourne-grove Bayswater in the County of Middlesex Banker in 1872
John James Martin of Belvedere Esquire the Sons in 1872
Mary Catherine Martin of Belvedere in 1872
Emily of Belveder, Christchurch in 1871

and in 1851 she had:

MARTIN, Charles W  Son   M  20  1831  East India Compy Artillery  Broam, East Indies
MARTIN, Mary C     Daur  F  18  1833  Scholar                     Broam, East Indies
MARTIN, George E   Son   M  17  1834  Naval Cadet                 Broam, East Indies
John J  Martin     Son   M  12  1839  Scholar                     Pendleton, Lancashire

and in 1861 there were:

Mary C.   b. 1833
Jane  S,  b. 1835
Emily L,  b. 1836

I can find no information about any of their marriages of Sarah’s offspring or, possibly, descendants.  There are just too many Martins with the same forenames in this universe.
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The probate Index for her is:

MARTIN, Sarah. 10 December [1872]  The Will of Sarah martin late of Belvedere in the Parish of Christchurch in the County of Southampton Widow who died 11 November 1872 at Belvedere was proved at Winchester by George Edward Martin of 74 Westbourne-grove Bayswater in the County of Middlesex Banker and John James Martin of Belvedere Esquire the Sons and Mary Catherine martin of Belvedere Spinster the Daughter the Executors.

This was identified as here from the other Sarah martin Probates by
1. He abode in Belvedere
2. Her daughter Mary Catherine

together with the census of 1871 which had:

1. Birth in 1799
2. Born in Checkley, Staffordshire
3. With her daughter Emily, found in previous censuses.
4. Living in Bwelvedere, Christchurch, Hants.
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Their marriage on Family Search:

Name Charles William Martin
Spouse's Name Sarah Charlewood
Event Date 03 Nov 1829
Event Place Checkley, Stafford, England

Indexing Project (Batch) Number M03779-1
System Origin England-ODM
GS Film number 426524
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