Her birth index, with the mother’s maiden name added from the printed index page:

Name:                                Mother's Maiden Surname:
ADDERLEY, MARY                      BIRKBECK
GRO Reference: 1922  D Quarter in MUTFORD  Volume 04A  Page 1746
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Burke reports: “b 8 Sept 1922; 3rd Offr WRNS WW II; m 7 July 1950 Hugh Montgomery-Campbell (d 1980), Capt RA WW II, only s of Rt Rev and Rt Hon Henry Colville Montgomery-Campbell, KCVO, MC, PC, DD, Bp London 1956–61, and has: [3 children]”
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Their three children were, noting the surname error for Veronica:

Last name             First name(s)  Year Of Birth  Location
Montgomery-Campbell   Philip H       1951           Westminster, London
Montgomery-Campbell   Elisabeth M    1954           Hampstead, London
Montogomery-Campbell  Veronica       1958           Marylebone, London

(I’ve told FindMyPast about Veronica’s surname)
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I cannot identify any death report, though she would only be 98 if still alive.
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Her probate index:

2019
          First       Date of                      Date of     Document
Surname   name        probate    Probate number    death       type      Registry
CAMPBELL  MARY        16 August  1562915947177538  30 January  Grant     Oxford
          MONTGOMERY  2019                         2019        and will

This has been ordered, to see what had become of her family.
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In the probate for her will, the executors were her children Veronica Berman and Philip Henry Montgomery Campbell, both living in England.  The reserve executors for Veronica were Jeffrey M Berman then Alexander Hugh Berman, both of the same address as Veronica.   The reserve executor for Philip was Simon Hugh Campbell (subsequently found to be Philip’s son).  She died at St Marys Convent & Nursing Home Burlington Lane London  W4 2QE.

her will, of 17 pages, was dated 23 Feb 2016.

In her will she left legacies to each of her children, already discovered, meaning that they were all alive in 2016.

Further she listed her grandchildren:
1.  Philip     }
    Veronica   } all, seemingly, Montgomery-Campbell.
    Elizabeth  }

2.  Simon                      }
    Christopher John Campbell  } all, seemingly, Berman
    Alexander                  }
    Nicholas Henry             }

(My guess from the above is that her daughter Elizabeth had no children.

The rest of her will and codicil was given to setting up of a complicated trust which did not mention any more relatives.
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Their marriage index:

First name(s)       Mary
Last name           Adderley
Marriage quarter    3
Marriage year       1950
MarriageFinder      Mary Adderley married one of these people
                    Hugh M Campbell
Spouse's last name  Campbell
District            Marylebone
County              London
Country             England
Volume              5D
Page number         795
Record set          England & Wales Marriages 1837-2005

FreeBMD shows that he was using the double barrel:

Surname        First name(s)  Spouse     District     Vol  Page
Marriages Sep 1950   (>99%)
Adderley             Mary     Campbell   Marylebone   5d   795
Campbell             Hugh M   Adderley Marylebone   5d   795
MONTGOMERY-CAMPBELL  Hugh     ADDERLEY Marylebone   5d   795
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