Her birth index:

First name(s) IDA MURIEL
Last name CAVE
Birth year 1907
Birth quarter 3
Registration month -
Mother's maiden name Childs
District Cambridge
County Cambridgeshire
Country England
Volume 3B
Page 430
Record set England & Wales Births 1837-2006

The new GRO indexes confirm her mother’s maiden name:

Name: Mother's Maiden Surname:
CAVE, IDA  MURIEL   CHILDS
GRO Reference: 1907  S Quarter in CAMBRIDGE  Volume 03B  Page 430
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In 1911 she was with her parents and siblings:

First name(s) Last name Relationship Marital status  Sex  Age  Birth year  Occupation  Birth place

Churles Cave Head Married Male 53 1858 Retired Army Warrant Officer And Clerical Work At Camb University Engineering Labey Munch Isle of Ely
Ada Cave Wife Married Female 44 1867 - Stock Essex
May W Cave Daughter Single Female 17 1894   -  Aldershot Hants
Henry W Cave Son - Male 13 1898 School Karacher India Resident
Alfred E Cave Son - Male 12 1899 School Balnchiston Quelta India Resident
Emily E Cave Daughter - Female 10 1901 School  Balnchiston Quelta India Resident
Percival G Cave Son - Male 8 1903 - Cambridge Cambridgeshire Resident
Ida M Cave Daughter - Female 3 1908 - Cambridge Cambridgeshire

Address: 29 Abbey Road Cambridge, Cambridge, Cambridgeshire

Ref: RG14PN9101 RG78PN483 RD181 SD1 ED1 SN201
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Might this be her in 1939:

Townsend Household (4 People)
10 The Homing , Cambridge M.B., Cambridgeshire, England

FIRST NAME(S) LAST NAME(S) DOB SEX OCCUPATION MARITAL STATUS  SCHEDULE  SCHEDULE SUB NUMBER
Ida M Townsend 23 Jul 1907 Female Unpaid Domestic Duties  Married  35  1
Sorry, this record is officially closed. Check if you can open a closed record.
Sorry, this record is officially closed. Check if you can open a closed record.
Donald M Gray 26 Jun 1919 Male ??? Single 35 4

Ref: RG101/6303C/004/23
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The above birth date corresponds with her age as given on her marriage certificate: 23 in 1931, giving a birth year of 1908

And might this be her death in 1975, the birth date is the same as in the 1939 record:

First name(s) IDA MURIEL
Last name TOWNSEND
Gender Female
Birth day 23
Birth month 7
Birth year 1907
Age -
Death quarter 3
Death year 1975
District Cambridge
County Cambridgeshire
Volume 9
Page 0545
Country England
Record set England & Wales Deaths 1837-2007
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If the 1939 and 1975 records are for George William’s wife, then her forenames are Ida Muriel.  An answer would be to get the marriage certificate; the bonus is that it might confirm that George was the son of his father.
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Her probate index:

TOWNSEND, Ida Muriel of 13 Mount Pleasant Cambridge died 13 July 1975  Administration Ipswich 21 November £6000  771010496H
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Their marriage, the only George W Townsend to be married in Cambridgeshire:

Surname   First name(s)   Spouse   District  Vol  Page
Marriages Jun 1931   (>99%)
Cave Ida M Townsend Cambridge 3b 1228
Townsend George W Cave Cambridge 3b 1228

But Ida M Cave is not on FreeBMD’s birth recordds.  But there was one on Scotland’s People:

No Year Surname Forename Sex District City/    GROS
                                              County/MR  Data

1 1900 CAVE IDA MARJORIE F STIRLING  /STIRLING  490/00 0080

But this conflicts with (a) her age of 23 recorded at marriage in 1931, her birth date in 1907 in the 1939 Register and her birth date recorded on her death index.  So this Scots birth in 1900 must be abandoned.
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There are three Townsend-Cave marriages in England and Wales from 1930 to 1950, though the last is female-male so not right:

Last Name First Name Born Died Event Location
Townsend George W — — 1931 Cambridge, Cambridgeshire, England
Townsend Ronald — — 1945 Brentford, Middlesex, England
Townsend Audrey V — — 1947 Lewisham, London, England

The third of these would be the parents of the Rodney Townsend born in Uxbridge district in 1950.

So it looks like George and Ida had but the one child.  Though there are two redacted (ie child) entries in the 1939 Register.

Remarkably, now that I have done all the above her birth clearly appears on FindMyPast.  See her Person Sheet Notes, etc.
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Their marriage certificate adds the following:

Marriage Cert no 248 on 1 June 1931 at Christ Church in the parish of St Andrew the Less, Cambridge.

                His                       Hers
Names           George William Townsend   Ida Muriel Cave
Ages            24                        23
Status          Bachelor                  Spinster
Job             Factory Hand              -
Residence       24 Norfolk Road           29 Abbey Road (she was living there in 1911)
Father          John Albert Townsend      Charles Cave
Father job      Cycle Agent               University Laby

Witnesses       F H Drane (husband of his sister Emily), C E Cave (her father?)

Celebrant       John E H Lebanrood
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