Her birth index:

First name(s) BRENDA E
Last name HARDING
Birth year 1932
Birth quarter 4
Registration month -
Mother's last name MAIDENS
District BEAMINSTER
County Dorset
Country England
Volume 5A
Page 431
Record set England & Wales births 1837-2006

Her birth certificate has been obtained and confirms her parents.
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I wonder if this Boston district marriage might be hers?

First name(s) BRENDA E
Last name HARDING
Marriage quarter 1
Marriage year 1954
Registration month -
MarriageFinder™ BRENDA E HARDING married
RONALD BARNES
Spouse's last name BARNES
District BOSTON
District number -
County Lincolnshire
Country England
Volume 3B
Page 25
Record set England & Wales marriages 1837-2008

Now that there is a chance she has descendants, her marriage cert is being ordered to see if it is her, from her father’s name.

The marriage certificate confirms that she was the daughter of her father.
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There are loads of Barnes births with Harding mothers from 1953 to 1973, but two of them are in Boston, so could be hers:

First name(s) MORRIS R
Last name BARNES
Birth year 1956
Birth quarter 1
Registration month -
Mother's last name HARDING
District BOSTON
County Lincolnshire
Country England
Volume 3B
Page 35
Record set England & Wales births 1837-2006

First name(s) SUSAN P
Last name BARNES
Birth year 1958
Birth quarter 1
Registration month -
Mother's last name HARDING
District BOSTON
County Lincolnshire
Country England
Volume 3B
Page 4
Record set England & Wales births 1837-2006

There are 11 other Harding births from 1953 to 1963: 3 in Kent, 3 in Gloucestershire, 2 in Bucks, 1 in Sussex and 2 in Somerset.  Some of them could also be of this marriage, of course.

The certificates for the two Boston registrations are being ordered.
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A Morris R Barnes was married in Boston in 1974 when he would have been 18; this is the only Morris marriage in England and Wales.

This marriage was:

First name(s) MORRIS R
Last name BARNES
Marriage quarter 2
Marriage year 1975
Registration month -
MarriageFinder™ MORRIS R BARNES married
GLENDA CLAYTON
Spouse's last name CLAYTON
District BOSTON
District number -
County Lincolnshire
Country England
Volume 7
Page 1048
Record set England & Wales marriages 1837-2008

There are 10 children born to Barnes-Clayton parents, of which two were in Boston:

First name(s) NICKY LEON
Last name BARNES
Birth year 1977
Birth quarter 4
Registration month -
Mother's last name CLAYTON
District BOSTON
County Lincolnshire
Country England
Volume 7
Page 1261
Record set England & Wales births 1837-2006

First name(s) BRENDON
Last name BARNES
Birth year 1983
Birth quarter 3
Registration month -
Mother's last name CLAYTON
District BOSTON
County Lincolnshire
Country England
Volume 7
Page 1681
Record set England & Wales births 1837-2006

Of the 8 other Barnes-Clayton births, 6 were in Wales, 1 in Lancashire and 1 in Leicestershire.

The above two Boston births look plausible, particularly if it can be established that Morris’ parents were correct.
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There are 15 marriages of Susan P Barnes.  Of these one was in Boston in 1980 when she would have been 22.  I suspect I will be ordering this certificate when her mother has been confirmed to be Brenda Elizabeth Harding.

The Susan P Barnes marriage in Boston was:

First name(s) SUSAN P
Last name BARNES
Marriage quarter 3
Marriage year 1980
Registration month -
MarriageFinder™ SUSAN P BARNES married
ANTHONY M PICK
Spouse's last name PICK
District BOSTON
District number -
County Lincolnshire
Country England
Volume 7
Page 1511
Record set England & Wales marriages 1837-2008

But no children can be found for this marriage from 1972 to 1999.
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Her possible, and early, death index, the only Brenda E Barnes death after 1958 to 2006, though she could still be alive:

First name(s) BRENDA E
Last name BARNES
Gender Female
Birth day -
Birth month -
Birth year 1933
Age 33
Death quarter 2
Death year 1966
District WALTHAM FOREST
County Essex
Volume 5E
Page 345
Country England
Record set England & Wales deaths 1837-2007

Note that this death was in the London area and she would hav e been a mere 33.  I am not think it was certainly her.  The second name on the will of this death was Eleanor, so it could not have been her.

So, in 2016, no death found.

(There were three Ronald Barnes marriages in Lincs after her death, which makes it more likely that she did die in 1966 and he then remarried.  The answer is to buy her death certificate.  If she did die early, this was another tragic generation of early parental deaths.)
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Their marriage certificate:

At St Mary the Virgin church, Frampton, Lincs.

cert No: 55
Date: March 20th 1954
His name: Ronald Barnes
His age: 24
His status: Bachelor
His job: Agricultural worker
His abode: Jail Lane, Frampton
His father: Edward Barnes
His father’s job: Farm labourer
Her name: Brenda Elizabeth Harding
Her age: 21
Her status: Spinster
Her job: Land(?) worker
Her abode: Frampton West
Her father: Theophilus Roland William Hector Harding
Her father’s job: Deceased

Witnesses:
  W E Barnes (probabbly a relation of the groom)
  K R Harding (the bride’s elder brother)
  M J Maidens (of the bride’s mother’s family)
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