Second cousin to her husband.

Her baptism from FamilySearch:

First name(s)           Frances
Last name               Powys
Gender                  Female
Baptism year            1816
Baptism date            06 Oct 1816
Residence               Titchmarsh, Northampton, England
Place                   Titchmarsh
County                  Northamptonshire
Country                 England
Father's first name(s)  Littleton
Father's last name      Powys
Mother's first name(s)  Penelope
Record set              England Births & Baptisms 1538-1975
_________________

No birth registrations found.  But these baptisms were found:

1839  Daniel                           at Rudgwick, Sx            (not their child)
1840  Frances Adamina Lucy             at Bowdon, Cheshire        downloaded
1841  Amelia Penelope                  at Bowdon, Cheshire        downloaded
1842  Mann  William Henry Galfridus    at Bowdon, Cheshire        downloaded
1843  Mann  Littleton Powys            at Bowdon, Cheshire        downloaded
1844  Mann  Marjory                    at Aberdeenshire Scotland  (Not their child)
1845  Horace Littleton                 at Bowdon, Cheshire        downloaded
1845  Mary                             at Rudgwick Sussex         (Not their child)
1847  Fanny Henriette                  at Bowdon, Cheshire        (Trancript downloaded)
1851 (or 7) Cornwallis Ernext Hatsell  at Bowdon, Cheshire        downloaded
1852  Alice                            at Spalding, Lincs         (not their child)
1852  Maria                            at Spalding Lincs          (Not their child)
1854  Gerard Llewelyn Noel             at Henllan, Denbigh        downloaded

That makes 8 children for them.  I wonder what the censuses tell us.
____________________

In 1851: they were at Vicarage and Moos Lane, Bowdon, Altrincham, Cheshire and she and her children were given the surname of ‘Marm’ and they had an enormous household:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
William Henry G         Mann     Head      M      M  57  1794  Vicar Of Bowdon  Linton, Kent
Frances                 Marm     Wife      M      F  34  1817  -                Titchfield, Northants
F adamison              Marm     Daughter  -      F  11  1840  Scholar          Bowdon, Cheshire
Amelia Penelope         Marm     Daughter  -      F   9  1842  Scholar          Bowdon, Cheshire
William Henry Galfidus  Marm     Son       -      M   6  1845  Scholar          Bowdon, Cheshire
Horace Littleton        Marm     Son       -      M   5  1846  -                Bowdon, Cheshire
Fanny Henrietta         Marm     Daughter  -      F   3  1848  -                Bowdon, Cheshire
Julia Lay               Bygrave  Servant   Un-m   F  21  1830  Governess        Little Baddow, Essex
Mary Ann                Ireland  Servant   Widow  F  46  1805  House Keeper     Gosport, Hampshire
Jane                    Edwards  Servant   Un-m   F  29  1822  -                Marylebone, Middlesex
Ann                     Bishop   Servant   Un-m   F  23  1828  Cook             Titchfield, Northants
Harriet                 Denston  Servant   Un-m   F  26  1825  Laundry Maid     Duffield, Derbyshire
Esther                  Hibbert  Servant   Un-m   F  24  1827  House Maid       Chapel-En-Le-Frith, Derbys
Eliza Ann               Seade    Servant   Un-m   F  21  1830  Nursery Maid     Weston Super Mare, Som
Margaret                Burks    Servant   Un-m   F  17  1834  Kitchen Maid     Salford, Lancashire
Charles                 Howse    Servant   Un-m   M  29  1822  Coachman         Suffolk
George                  Howse    Servant   Un-m   M  14  1837  Page             Walsham Le Willows, Suffolk

Ref:
Archive reference  HO107
Piece number       2162
Folio              343
Page               27
Combined:          HO107, piece 2162, folio 343, p. 27

Littleton Powys is not found in this census.  The civil death records show he died in 1844.
___________________

In 1861 they were at 1, Park Street, Walcot, Bath, Somerset and he, at 67, had retired, they now had two more sons.  Curiously the George Dewhurst visitor becanme the husband of Frances Adamina Lucy and month or so later but where was she?   Littleton Powys has died an infant and thus the seven other children found in the baptism records are confirmed between the 1851 and 1861 the censuses, the latter being:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
William H G     Mann      Head      Married    Male    67  1794  Clergyman Without Cure Of Souls
                                                                                       Linton, Kent
Frances         Mann      Wife      Married    Female  44  1817  -                     Titchmarsh, Northants
Frances         Mann      Daughter  Unmarried  Female  21  1840  -                     Bowdon, Cheshire
Amelia          Mann      Daughter  Unmarried  Female  19  1842  -                     Bowdon, Cheshire
William H G     Mann      Son       Unmarried  Male    18  1843  Scholar               Bowdon, Cheshire
Horace          Mann      Son       Unmarried  Male    15  1846  Scholar               Bowdon, Cheshire
Fanny           Mann      Daughter  Unmarried  Female  13  1848  Scholar               Bowdon, Cheshire
Cornwallis G H  Mann      Son       Unmarried  Male     9  1852  Scholar               Bowdon, Cheshire
Gerard L C H    Mann      Son       Unmarried  Male     7  1854  Scholar               Denbighshire, Wales
George          Dewhurst  Visitor   Unmarried  Male    21  1840  Commission Agent Cotton Trade
                                                                                       Manchester, Lancashire
Emma            Kimber    Servant   Unmarried  Female  27  1834  Domestic Servant      Woolley, Somerset
Dorcas          Burgess   Servant   Unmarried  Female  21  1840  Domestic Servant      Frome, Somerset
Hannah          Clark     Servant   Unmarried  Female  20  1841  Domestic Servant      -
John            Lloyd     Servant   Unmarried  Male    13  1848  Page                  St Asaph, Denbighshire,

Ref:
Archive reference  RG09
Piece number       1695
Folio              97
Page               24
Combined:          RG09, piece 1695, folio 97, p. 24
_______________________

In the 1881 census he was living, retired and without cure of souls, at Glaullyn, St Asaph, Denbigh, Wales with this household:

Name Relation Marital Status Gender Age Birthplace  Occupation  Disability

W. Henry G.  MANN       Head  M  Male    87  Linton, Kent             Clergyman (Without Cure of Souls)
Frances      MANN       Wife  M  Male    64  Titchmarsh, Northants    Clergymans Wife
Amelia P.    MANN       Daur  U  Female  39  Bowden, Cheshire         Clergymans Daur
Horace L.    MANN       Son   U  Male    35  Bowden, Cheshire         Farmer of 89 Acres Employing 2 Men
Fanny H.     MANN       Daur  U  Female  33  Bowden, Cheshire         Clergyman’s Daur
C. Ernest H. MANN       Son   U  Male    29  Bowden, Cheshire         Agent for Telephone Co
Mary         ROGERS     Serv  U  Female  24  Cheswardine, Shropshire  Cook (Domestic Serv)
Eliza        TAYLOR     Serv  U  Female  23  Chetwynd, Shropshire     Housemaid (Domestic)
Annie A.     STARTIN    Serv  U  Female  20  N K, Stafford            Waitress (Domestic)  
Annie M.     PHILLIPS   Serv  U  Female  18  Kingswinford, Stafford   Serving Maid (Domestic)  
Emily        MANSFIELD  Serv  U  Female  15  Ashbourne, Derby         Scullery Maid (Domestic)
_______________________

Their marriage transcription on FamilySearch:

Name:                    William Henry Galfredus Mann
Event Type:              Marriage
Event Date:              3 Jul 1838
Event Place:             Titchmarsh, Northamptonshire
Gender:                  Male
Father's Name:           James Mann
Spouse's Name:           Frances Powys
Spouse's Gender:         Female
Spouse's Father's Name:  Littleton Powys

with:

Document Information:
GS Film Number                   1999988
Digital Folder Number            004011466
Image Number                     00119
Indexing Project (Batch) Number   I04444-0
System Origin                    EASY
Record Number                    2
__________________

And from the copy of the register page:
                                    Him                            Her
Ages:                      Full                               Full
Condition:                 Widowr                             Spinster
Profession                 Clerk                              -
Residence                  Bowden Cheser(?)                   Titchmarsh
Father’s Profession        Esqre                              Clerk
Witnesses                  Littleton Powys Jnr, James Hatsell
Officiant                  Littleton Powys (Snr)
____________________