Her very probable baptism from FindMyPast:

Name: Catherine Wigley
Gender: Female
Christening Date: 22 Aug 1771
Christening Date (Original): 22 AUG 1771
Christening Place: SAINT ANDREW,PERSHORE,WORCESTER,ENGLAND
Birth Date: 10 Jul 1771
Father's Name: Henry Wigley
Mother's Name: Mary

If the above is correct, she would have been 26 at marriage.  At least the baptism place is in the same county as her later marriage.
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In 1851, she was part of the household of her daughter Sarah:

First name(s) Last name Relationship Marital status  Sex  Age  Birth year  Occupation  Birth place
Robert Burnett Brander Head Married Male 55 1796 Fund Holder & Land Proprietor  -
Sarah Brander Wife Married Female 44 1807 - Hornsey, Middlesex
Mary Brander Daughter - Female 18 1833 - South Lambeth, Surrey
Catherine Stjohn Mother Widow Female 81 1770  Fund Holder & Land Properietor  Pensham, Worcestershire
Eliza Kimber Servant Unmarried Female 30 1821  Servant  Hungerford, Berkshire
Charlotte Pulford Servant Unmarried Female 21  1830  Servant  Hastings, Sussex
Edward Shoesmith Servant Unmarried Male 20 1831  Servant  Bexhill, Sussex

Address & Ref
Street Maze Hill
Town Saint Leonards
Parish Saint Mary Magdalen
City Hastings
County Sussex
Archive reference HO107
Piece number 1635
Folio 524
Page 50

1851 Ref: HO107, Piece 1635, Folio 524, p. 50
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Might this be her death:

First name(s) CATHERINE
Last name ST JOHN
Gender Female
Death quarter 3
Death year 1856
District B righton
County Sussex
Volume 2B
Page 94
Country England
Record set England & Wales Deaths 1837-2007

and from the GRO site with her age:

Name: Age at Death (in years):
ST JOHN, CATHERINE     85
GRO Reference: 1856  S Quarter in BRIGHTHELMSTON  Volume 02B  Page 94

The age of 85 gives a birth year of 1771, the which corresponds with the above.

The PDF of her death certificate gives also:

Date: 23rd July 1856
Place: 11 Arundel Terrace [Kempstown, Brighton, Sussex]
Name: Catherein St John
Rank: Widow of Henry St John Gentleman
Cause: Apoplexy, 13 days Paralysis & Exhaustion Certified
Inform: Eliza Kimber Present at the death, 11 Arundel Terrace, Brighton
Reg Date: Twenty fifth July 1856
Registrar: Chas Humbrell, Registrar

Eliza Kimber is also to be found in the 1851 census in the household of Catherine’s daughter Sarah.
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No will found either on PCC or the probate registry.
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Might this be her will?

Reference: PROB 11/1511/163
Description: Will of Mary Wigley of Claines , Worcestershire
Date: 09 May 1810
Held by: The National Archives, Kew
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Marriage transcript on FamilySearch:

Name: Henry St John
Spouse's Name: Catherine Wigley
Event Date: 25 Apr 1797
Event Place: Claines,Worcester,England