She was only found initially in the 1881 census, which did not give her surname.  But she and Charles had her brother staying with them, surnamed Woods.  Later their marriage index record was found that confirmed she was Mary Ann Woods.

There are loads of Mary Ann Woods births from 1856 to 1860. The following are born in Middlesex from 1857 to 1860:

Surname  First name(s)      District           Vol  Page
Births Mar 1857
Woods Mary Ann Knowles    Chelsea            1a  154
Births Sep 1857   (96%)
Woods Mary                Clerkenwell        1b  495
Births Mar 1858
Woods Mary Ann            Mile End Old Town  1c  554
Woods Mary Sophia         Uxbridge           3a  34
Births Jun 1858
Woods Mary Ann            Kingston           2a  169
Births Dec 1858  
Woods Mary Ann            St Luke            1b  594
Births Dec 1860
WOODS Mary Ann            Bethnal Gn         1c  311
WOODS Mary                Mile End           1c  574

She could be any of the three born in 1958.
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There was a Mary Annie Sktchley who d. Q1 of 1883 in Leicester district on FreeBMD, but I don’t think it is her.
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In 1881 she had her brother staying with her; this may help to find their parents in 1871:

Name  Relation  Condition  Sex  Age  Birth Year  Occupation  Disability  Where Born

POWYS, Charles L  Head  M  M  29  1852  Clerk In Carpet Warehouse  Bangalore, East Indies
POWYS, Mary Ann   Wife  M  F  22  1859                             London, Middlesex
WOODS, Thomas     Bro   S  M  11  1870  Scholar                    London, Middlesex.

RG number: RG11  Piece: 19, Folio: 15, Page: 26    

Registration District: Pancras Sub District: Gray's Inn Lane Enumeration District:
Ecclesiastical Parish:

Civil Parish: St Pancras Municipal Borough:
Address: 11, Frederick St, St Pancras
County: Middlesex
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In 1894 a Mary Anne Powys died in Marylebone aged 82, but that is far too old.

I can’t find a Mary Ann who died between 1877 and 1889 and was between 20 and 30, though there was a Mary Ada who d. in 1877 aged 20 and might have been the right person apart from the appearance in the 1881 census with her brother.

Nor can I find a second marriage for Charles.  Weird.

Though there was a Mary Ann Powys, widow, who was born in London in 1866 in Lambeth in 1911 but there was no entry of any death of such a lady on FreeBMD up to c. 1935.

I have been through the 1871 census for a possible Woods family that included Mary (Ann) aged 12 and Thomas aged 1 and where both these children were born around London.  I found nothing.
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She survived at least until 1911 (Oh!  Can’t find her on The Genealogist).  There is but one Mary A Powys death after that from FreeBMD up to c. 1950:

Surname  First name(s)  Age  District  Vol  Page
Deaths Sep 1926   (>99%)
Powys    Mary A         66   Neath     11a  717

But this was more likely to have been the Mary Ann Powys in the 1911 census as born in 1861 who was married to a Benjamin Powys and born in Aberdare, Glamorgan.
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Their marriage index:

Surname  First name(s)    District   Vol  Page
Marriages Dec 1877   (>99%)
DAVIS  Eliza Ann          St. Giles  1b   925
Payne  Thomas             St. Giles  1b   925
Powys  Charles Lyttelton  St. Giles  1b   925
Powys  Charles Lyttleton  St. Giles  1b   925
Woods  Mary Ann           St. Giles  1b   925
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