Today, the address on Barbara's birth is known as Woburn Court, 53-55 St Bernard Street. It was a boarding house in 1911 too, owned by a Fanny Nelson - one extra census page just full of boarders and servants.
Noting: on the 1922 marriage index , Frances is "Cowin" - or Knights - with an 's".
Now, this is left-field............Henry Cowin, Electrical engineer, the year after the war ended.
Geoffrey Chevell Lawrence, was in a similar line of work........Engineer. Graduated from Durham University, Mechanical Engineering, Marine Engineering. In 1917 described as fit in all aspects for --- capable of performing the duties of an Engineer Officer in charge of Machinery on a small Navy ship. He has in due course, attained power of command over men and has above average
officer qualities. Zealous. Capable.....
Born 6 Sep 1887 Bury St Edmonds, Suffolk, enlisted in the RN on 26 Aug 1916
Entered with Seniority, Eng Sub Lt
Served in the Home Fleet until end of war. Last ship appointed to, 5 Apr 1919
Demobilised 19 Apr 1919
Re-entered as Special Reserve 20 Apr 1920, Engineer Lt, until 1932.
Perhaps should explore the possibility that Henry Cowin and Geoffrey C Lawrence could be one and the same man? Which is where a DNA test for OP's father would come in doubly handy.
And as chatter Jorose asked of the OP above, the details of the 1922 marriage cert & the 1919 birth may hold many clues - particulary interested re her father's name in 1922, who informed 1919 and - also the spelling of Henry's name as COWAN or COWIN
Cheers
AMBLY