Her birth registration:

Surname   First name(s)      District   Vol  Page
Births Dec 1879   (>99%)
Bartholemew Beatrice Elizabeth Mildenhall 4a  595
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In the 1901 census she had her first dau:

Surname  Forename  Age  Relation  Occupation  Birth Place

Harris William C 25 Head Stableman Groom Landreath, Cornwall
Harris Beatrice E 21 Wife Kentford, Suffolk
Harris Beatrice T 3M Daughter Newmarket, Cambridgeshire

Ref: RG13/1541/~F165

Address: Park Lane Park Cottage
Parish: Newmarket All Saints
Registration District: Newmarket
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In 1911 she had 6 children and stated that was all that she had with all living after 11 years of marriage:

Surname  Forename  Age  Gender  Relation  Marriage Status  
Years Married  Occupation  Birth Place

Harris William C 34 Male Head Married 11 Head Man Racing Stables (Groom) Lanreath, Cornwall
Harris Beatrice E 31 Female Wife Married 11 Kentford, Suffolk
Harris Beatrice J 10 Female Daughter Single - Newmarket, Cambridgeshire
Harris William A 8 Male Son Single - Newmarket, Cambridgeshire
Harris Claud M 5 Male Son Single - Newmarket, Cambridgeshire
Harris Charles C 4 Male Son Single - Newmarket, Cambridgeshire
Harris Amy E 2 Female Daughter Single - Newmarket, Cambridgeshire
Harris Regenild L 10 M Male Son Single - Kentford, Suffolk

Reference: RG14 - PN9182 RD183 SD2 ED6 SN274

Address: St Albans Cottage, Newmarket, Suffolk
Registration District: Newmarket
Sub District: Newmarket
Civil Parish: Exning
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There are 40 Beatrice E Harris deaths on The Genealogist from 1940 to 1980 (when she would have been 100):

Name Beatrice E Harris
District Cambridge, Cambridgeshire
Date of Birth 1874
Page 0262
Volume 4A
Registered January - March 1957

Name Beatrice E Harris
District Evesham, Worcestershire
Date of Birth 1876
Page 0098
Volume 9D
Registered October - December 1952

Name Beatrice E Harris
District Norwich Outer, Norfolk
Date of Birth 1876
Page 0662
Volume 4B
Registered April - June 1961

Name Beatrice E Harris
District Surrey North Western, Surrey
Date of Birth 1880
Page 0726
Volume 5G
Registered October - December 1956

Name Beatrice E Harris
District Honiton, Devon
Date of Birth 1881
Page 0545
Volume 7A
Registered January - March 1959

Name Beatrice E Harris
District Essex South Western, Essex
Date of Birth 1881
Page 0135
Volume 5A
Registered April - June 1963

But none of their birth dates are close enough to be confident.
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Their marriage registration:

Surname   First name(s)      District   Vol  Page
Marriages Mar 1900   (>99%)
Bartholomew Beatrice Elizabeth Newmarket 3b  692
Harris William Charles    Newmarket 3b 692
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