If her birth was registered, this is the only possible birth on FreeBMD, though it is a bit late and E London is not quite the same as the Essex of the 1881 census:

Surname  First name(s)   District   Vol   Page 

Births Jun 1858   (>99%)
Walmsley Mary E.London 1c 14
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In the 1861 census, this is a possibility for her but bother her parents were out of the house:

Surname   Forename   Age   Relation   Occupation  Birth Place
Walmsley Mary N E(?) 44 Head Wine merchant’s wife  Bloomsbury, Mx
Walmsley Mary 15 Daughter Scholar Romford, Essex
Walmsley Josephine 3 Daughter Stock, Essex
Keddle Francis 46 Serv Nurse Domestic Colchester, Essex
Wright Catherine 26 Serv Cook Domestic Corly, Lincoln
Wright Jane 24 Serv Housemaid Domestic Boston, Lincoln
Palvia Celina 31 Serv Lady's Maid Domestic   -, France

Address: 7 Berkeley Gardens
Registration  District: Kensington, Middlesex
Parish:
Image Reference: RG10/0032/~F70

However the enumerator’s sheet in fact includes their mother so I have included her details above.

The daughter Teresa who is in the 1881 census is to be found as a pupil in a convent for this census.

Assuming the above is her family, I suppose her father might have been abroad on his wine business.
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Their marriage:

Surname First name(s) District Vol  Page
Marriages Mar 1877   (>99%)
Allen Emmalina Marylebone 1a 871
BELLASIS William Marylebone 1a 871
Butler Thomas Marylebone 1a 871
Walmesley Mary Marylebone 1a 871
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