Background:

In the 1970s we knew:  Probate, in the year 1939 Admons.:

"SWEETMAN Georgina Elizabeth of 42 Chichester-Road Kilburn Middlesex, Widow, died 13 June 1939. Administration London 3 August to Rosa Elizabeth Wilson (wife of Clement Sydney Wilson). £486 18s 4d.
To  Rose Elizabeth Wilson, 15 Worton Way Hounslow, Lawful niece of the whole blood and one of the persons entitled to share in the estate of the said intestate.
Filed by:  Mssrs. Sidney Smith Son & Leefe,  42 Kilburn High Road  NW6"

    So we figured that if Rose or Rosa Elizabeth Wilson was a full niece (lawful of the whole blood) she would have to be a daughter of a brother or sister, of Georgina Elizabeth Foulger (henceforth GEF).   If Rose or Rosa was a daughter of a brother of GEF her maiden name would be Foulger so we can look for a marriage of Rose or Rosa Elizabeth Foulger to Clement Sydney Wilson.  However we couldn't find any brother of GEF.   If Rose or Rosa was the daughter of a sister, she could have any maiden name, but her mother's maiden name would still have to be Foulger. Also the name Wiskin poped up as a possibility so she might have been Rose or Rosa Elizabeth Wiskin.  In any case although Wilson is a common surname and difficult to search Clement is not a common forename, so we tried Clement Wilson.  It is easier to work from someone backwards rather than forwards, so perhaps try first for all the marriages of Clement Wilson and check for Rose or Rosa Elizabeth Foulger or Wiskin in particular.  They must have been married by 1939 and ERWT says well before, so search for marriages of Clement Wilson (particularly to Rose or Rosa anything, possibly Foulger or Wiskin):
 

Marriages of Clement Wilson:
 

Start  1900, all grooms surnames' are Wilson.  No partners surnames are given before 01/01/1912
1901	MQ	Clement Goldsmith = ? at Norwich, NOT Foulger or Wiskin
1904	SQ	Clement Frederick + ? at King's Norton,  NOT Foulger or Wiskin
1904	DQ	Clement Eustace M = ? at Westminster,  NOT Foulger or Wiskin
1905	SQ	Clement = ? at Stoke on Trent,  NOT Foulger or Wiskin
1905	SQ	Clement Ralph = ? at Hackney,  NOT Foulger or Wiskin
1908	SQ	Clement = ? at Huddersfield,  NOT Foulger or Wiskin
1910	JQ	Clement = ? at Fylde,  NOT Foulger or Wiskin
1910	SQ	Clement = ? at Fylde,  NOT Foulger or Wiskin
1911	SQ	Clement D. = ? at Middlesborough,  NOT Foulger or Wiskin
1911	DQ	Clement = ? at Kendal 10b 1313,  NOT Foulger or Wiskin
1912	JQ	Clement E.M. = Adele G.A. Hamilton at Wem 6a 1639
1912	JQ	Clement = Annie Roebuck at Halifax 9a 986
1916	SQ	Clement J. = Miss Wilson (NOT Rose/a) at W. Ham 4a 513
1917	SQ	Clement W. = Miss Williams (NOT Rose/a) at Rugby 6d 1490
1920	JQ	Clement = Mary J. McClenning at Lanchester 10a 850
1920	DQ	Clement = Miss Smith (NOT Rose/a) at Halifax 9a 1129
1922	JQ	Clem F. = Miss Robinson (NOT Rose/a) at Rye 2b 11
1922	DQ	Clement = Nellie Brearley at Huddersfield 9a 815
1923	DQ	Clement S.L. = Miriam M. Handley at Headington 3a 2334
1926	MQ	Clement = Janet Lofthouse at ???
1927	MQ	Clement E. = Annie Hardwick at Chesterfield 7b 1164
1927	JQ	Clement R. = Glayds E. Hall at Kingston 2a 1083
1928	MQ	Clement = Alice Savage at Stockton 10a 121
1928	SQ	Clement G. R. = Emeline Hitchin at Prescot 8b 1593
1929	SQ	Clement = Rose A. Reynolds at Hackney 1b 1305  (see NOTES below)
1931	JQ	Clement T. = Miss King (NOT Rose/a) at Edmonton 3a 1682
1931	DQ	Clement V. = Miss Carter (NOT Rose/a) at Rochford
1931	DQ	Clement M. = Miss Johnston (NOT Rose/a) at Lewisham
1937	SQ	Clement N. = Lily Richardson at Newcastle upon Tyne
1937	DQ	Clement A. = Lilian K. Lofty at Aldershot
Up to the end of June 1939

NOTES:
    So the only possible candidate above was the SQ 1929 marriage of Clement Wilson to Rose A. Reynolds in Hackney.   The certificate says Rose Adelaide Reynolds, Widow age 44, of West Hackney, father Frederick Oakhill (Lithographic Artist) marries Clement Wilson, Bachelor age 49 Commercial (?) Clerk of Stoke Newington.  So back to search for the birth certificate of Rose Adelaide Oakhill in Smeanton, Nottingham in 1884 where her mother is Louisa Oakhill formerly Roe (NOT Foulger, which she would have to be for this Rose to be a proper niece).  Thus there is no indication whatsoever that this could possibly be the right Rose Wilson.

I really can't see any of the others above being likely.
 

Where to next?

Could Rose have married Clem Wilson either before 1900 or after June 1939, either seems unlikely. To be married before 1900 they would have to be at least 65 after the war when ERWT visited them. The probate details already detail them as married in 1939 when the documents were drawn up.
Could they have married outside of England and Wales?  This seems unlikely.  I could have missed it in the index, but unlikely because Clement is so rare.  If Clement Sydney Wilson was indexed as anything other than Clement (for instance if he was really Sydney Clement Wilson) I would have missed him - there are too many Wilsons to search them all.
Could I assume that Rose Elizabeth Wilson's maiden name was either Foulger or Wiskin and search for both of those - a long slog, but at least both surnames are less common than Wilson.
 

Censuses etc.

We know that GEF was at Canon Terrace Willesden with her parents and her sister Catherine age 21 in 1881.

The 1861 census at Quarlston Street also lists a sister Harriet (born about 1843/4 in Harleston - the large town next to Redenhall where her parents were married in May 1842).  However the following entry is confusing (see link) because it lists Rosa M. age 19 (hence born about 1841/2 in Marylebone, Middlesex) a scholar.  This is all fine IF the age is mis-recorded (and I note that the order is wrong and 19 year olds are not usually scholars in 1861) - I suspect it might be a mistake for 9 - I could check for the birth of Rosa M. Foulger in Marylebone (say 1840 to 1851).

So either Caroline or Harriet or Rosa M. might be Rose Wilson's mother?  However even finding their marriages would still leave an enormous amount more to do (search for the birth of a Rose/a with their married surname - impossible for common surnames) unless I know Rose Wilson's maiden name.

GEF wasn't even born by 1851, and I've no idea where her parents were at that census (except that they were NOT in Norfolk), so I can't see that much would be gained from searching for that, except to confirm the age of Rosa M.   Also to check the names of siblings of GEF it might be worth searching for the 1871 census?
 

1861 census for GEF and family at Quarlstone Street, Marylebone.

1881 census for GEF and family at Canon Terrace Willesden.
 

Wiskin
The Wiskin rumour always seemed to come from the Bungay area, and since Catherine was even born in Middlesex that seems unlikely.  We know that George Foulger and Harriet Reeve married 17/40/1842 in Redenhall in Norfolk (not that far from Bungay in Suffolk) and there is no sign of them in the 1851 census of Norfolk (and not much in the way of Wiskin in Norfolk in 1851).  So Wiskin is not GEF's mother's maiden name either (but could well be the married name of a sister of either George Foulger or Harriet Reeve - they were both born in Norfolk.
 

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