Her birth index:

First name(s) MARY LUCY O
Last name SETON
Birth year 1890
Birth quarter 3
Registration month -
Mother's last name -
District LEIGH
County Lancashire
Country England
Volume 8C
Page 254
Record set England & Wales births 1837-2006
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This may be her marriage:

First name(s) MARY L
Last name SETON
Marriage quarter 1
Marriage year 1922
Registration month -
MarriageFinder™ MARY L SETON married
PERCY J RELYEA
Spouse's last name RELYEA
District CHELSEA
District number -
County London
Country England
Volume 1A
Page 657
Record set England & Wales marriages 1837-2008
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No death found under the surnames of Seton and Relyea.

Subsequently an overseas marriage was found:

First name(s) MARY L O
Last name SETON
Year range 1921-1925
Marriage place BAGHDAD
Country IRAQ
Record Source GRO Consular Marriages (1849-1965)
Volume 18
Page 383
Record set British nationals married overseas 1818-2005

I think this really does need a certificate to get the name of her husband.

However I have also found these entries in that record set, they has the same volume and page numbers:

First name(s) ANDREW G H
Last name SIEVWRIGHT
Year range 1921-1925
Marriage place BAGHDAD
Country IRAQ
Record Source GRO Consular Marriages (1849-1965)
Volume 18
Page 383
Record set British nationals married overseas 1818-2005

First name(s) ROBERT S M
Last name STURGES
Year range 1921-1925
Marriage place BAGHDAD
Country IRAQ
Record Source GRO Consular Marriages (1849-1965)
Volume 18
Page 383
Record set British nationals married overseas 1818-2005

This looks like two marriages per page...

No children to either potential husband can be found.

Finally I noticed that the hardcopy of the index page included the surname of the spouse, which was:  Sievwright.
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She and Andrew are on the 1939 register, giving their birth dates:

Sievwright Household (4 People)
"Whistlers" Bransgore , Ringwood and Fordingbridge R.D., Hampshire

FIRST NAME(S) LAST NAME(S) DOB SEX OCCUPATION MARITAL STATUS  SCHEDULE  SCHEDULE SUB NUMBER

Mary L O Sievwright 09 Jul 1890 Female Wife Of Government Officer  Married  14  3
Andrew G H Sievwright 19 Feb 1885 Male Indian Government Officer  Married  14  1
Richard Spreckley 16 Aug 1894 Male Domestic Service Cook  Married  14  4
Rose C Spreckley 18 Dec 1902 Female Domestic Service J?  Married  14  5

Note that the above says that the household contained four people.  However there is one line redacted within the four people listed and three lines redacted afterwards, indicating that there may, just, be some children or a few young servants or visitors.
__________________

On FindMyPast it has three India Office births, all in 1944 or after, so they might be impossible for Mary to have been involved with her birth in 1890.  The mother’s names are not given.
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Her death on Scotland’s People:

  Surname/                                          S  A             City    
Year   /Maiden  Forename           Mother's   Other     e  g  District  County/   GROS
        Name                        Surname   Surnames   x  e              MR      Data

1983 SIEVWRIGHT MARY LUCY OGILV Not Permissible SETON F 92  ABOYNE  /ABERDEEN  330/00 0031

No probate entry found.
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Their marriage index transcriptions on FindMyPast:

First name(s) MARY L O
Last name SETON
Year range 1921-1925
Marriage place BAGHDAD
Country IRAQ
Record Source GRO Consular Marriages (1849-1965)
Volume 18
Page 383
Record set British nationals married overseas 1818-2005

The image of the source index sheet for Mary Seton in fact included the surname of her husband:  Sievwright.

First name(s) ANDREW G H
Last name SIEVWRIGHT
Year range 1921-1925
Marriage place BAGHDAD
Country IRAQ
Record Source GRO Consular Marriages (1849-1965)
Volume 18
Page 383
Record set British nationals married overseas 1818-2005

A marriage certificate is needed to give the actual date and year.
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