This is her probable birth, though it could be a year earlier than her census record:

First name(s) Winifred Ellen
Last name Matheson
Registration year 1876
Registered quarter/year 1876
Registration district Belfast
Volume 6
Page 310
County Antrim, Down
Country Ireland
Record set Irish Births 1864-1958
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Her marriage to one of these two chaps:

Surname First name(s) District Vol Page
Marriages Mar 1909   (>99%)
GARD Frederick Plymouth 5b 392   
HANSFORD William Plymouth 5b 392   
MATHESON Winifred Rose Plymouth 5b 392   
STONEMAN Alice Maud Plymouth 5b 392

But I can find her under neither surname in 1911...

But this marriage is not hers: (a) the second initial is wrong, (b) she died with her maiden name.
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In 1939, giving her birth date:

33 Vicarage Court , Kensington, London, England

FIRST NAME(S) LAST NAME(S) DOB SEX OCCUPATION     MARITAL STATUS  SCHEDULE  SCHEDULE SUB NUMBER
Winifred E Matheson 31 May 1876 Female Private Means  Single          87        1

She had a redacted younger person living with her.  Might this be the Ethel Gladys Matheson who obtained a Sealing at Winifred’s death?

There was an Ethel G Matheson who died in 1968 and was born, poss with a maiden name, in 1892

And in Q1 of 1911 an Ethel G matheson married one of Neil McColl and Lionel G Trower.  The 1911 census reveals that her husband was Lionel George Trower aged 53 and a stock exchange worker.
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Her death index:

First name(s) WINIFRED E
Last name MATHESON
Gender Female
Birth year 1876
Age 84
Death quarter 2
Death year 1960
District Kensington
County London
Volume 5C
Page 1002
Country England
Record set England & Wales Deaths 1837-2007
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Her probagte index:

MATHESON Winifred Ellen of 73 Vicarage Court Kensington Church Street London died 9 May 1960  Confirmation of Ethel Gladys Matheson
Sealed London 20 October.
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