Details are not clear but she went to a college of art in London and followed that with a career in dress designing in London until she went to Ceylon to join her husband in 1947.

She returned to the family home in Downend near Bristol after the deaths of both her husband and her father within a few months of one another.  She and her also widowed sister then shared the two halves of the semi.

Later note by TFPL: her father died c. Feb 1952 and her husband in 1952, so it was more than a few months.
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Jan 2008, As yet no sign of her 1916 birth, even just the surname Longden, on FreeBMD.  But, in Sep 2009 FreeBMD had:

Surname First name(s) Mother District Vol Page
Births Dec 1916
Longden Edna L Phillips Monmouth 11a 58   
Births Jun 1917
Longden Gladys W Jones Cheltenham 6a 613   
Births Mar 1918  
Longden Dora E Stafford Keynsham 5c 686   
Births Sep 1918
Longden Rhoda G Phillips Monmouth 11a 62

Looks like someone got her year of birth wrong.  Or, unlikely, she was registered a year late.

Anyhow this led to finding her sister:

Surname First name(s) Mother District Vol Page
Births Sep 1914  
Longden Edna G Stafford Keynsham 5c 927   
Births Mar 1918
Longden Dora E Stafford Keynsham 5c 686
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TFPL, Aug 2019: I have her birth date down as 26 Dec 1916.

But in the 1939 Register, when she was in London and within a year of her marriage her birth date is shown as 29 Dec 1917.  This latter date ties in with her birth registration in Q1 of 1918.  So I am inclined to categorise the 1916 date as horse whispers.  

In 2005 when she died, the registrar was informed, possibly with a birth certificate, that Dora had been born on 29 Dec 1917, as in this death index entry:

First name(s) EILEEN DORA
Last name POWYS-LYBBE
Gender Female
Birth day 29
Birth month 12
Birth year 1917
Death quarter 4
Death year 2005
District South Gloucestershire
District number 3041D
Register number D21
Entry number 219
Date of registration mm/yy 1005
County Gloucestershire
Country England
Record set England & Wales Deaths 1837-2007

So we have two official birth dates the same, contradicitng one of unknown source and which last is negatived also by the registration quarter.  Therefore I am changing her birth date from 26 Dec 1916 to 29 Dec 1917.

Note that at death her forename order was reversed from that in the birth index and in the 1939 Register.  Heaven knows why!

Just to make the issue a little more hilarious, I find that there are two versions of her page of the 1939 register, in different hands.  One is 90% redacted, the other 3% so they can't be totally compared to find if there are any differences.  Dora's line is in clear on both.  Anyhow HER birth date is the same on both.  Phew!
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Their marriage on FreeBMD:

Surname   First name(s)   Mother/Spouse/Age   District   Vol  Page
Marriages Dec 1940   (>99%)
Longden Dora E Pavys-Lybbe Portsmouth 2b 1679
Lybbe Roy A P Longden Portsmouth 2b 1679
Powys-Lybbe Roy A Longden Portsmouth 2b 1679