Have you tried Genes Reunited? When I was looking for my family they were on Genes Reunited looking for me.
There are 396 Muriels married in London between 1943 and 1953, a bit of a difficult task I think and it cannot even be certain she was adopted in London. I was born in Suffolk and adopted in Petersfield Hants.
It is possible she retained her name. A non variant search produces just 2 Muriel Beales, one of whom was noted in the 1939 register associated with the name Kerr.
There is a Kerr/Beale marriage in 1943 and a Kerr death on 2005 which looks as if it is the same person.
As you are aware I am in touch with you so i am just adding this here to show your question has not been ignored.