I've found her! Meg that is. Here is all I could find online.
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We have a certain fondness for Meg. I think we first saw her at Bunjies in the late sixties. It would have been one of the nights that Hratch was performing. There would be this noisy bustling as Meg moved through the tightly packed audience. Newcomers to Bunjies would have wondered what had descended upon them. We regulars knew that Hratch's performance would be interrupted whilst Queen Busker sang her repertoire. She had to get on with things as there would be many more venues that night for her to 'ply' her vocals!

Her 'uniform' was a threadbare fawn coat and silk headscarf which she was constantly adjusting. Her mouth was sorely lacking in teeth which accounted for phrases like 'fly away' being uttered as 'ply away'! Her soprano voice however was oh so very sweet. She used to relate the story of how Gracie Fields once threw money at her in 1946 when she was busking for the Prince of Wales theatre queue. It was never clear whether this act of Gracie's was to encourage more singing or to suggest a cessation! There are lots of stories about Meg but one we know to be fact ('cos we were there) is her impromptu performance with Simon and Garfunkel at the Royal Albert Hall in May 1968. I seem to recall only three songs in her repertoire: 'Danny Boy, 'The last thing on my mind' and 'I'll fly away'

In 1974 Meg was crowned Queen of the Buskers by the London Tourist Board. An accolade richly deserved. She also appeared in the film 'Darling' which was a cynical look at the 'Swinging' '60s
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I'm pretty sure she was sleeping rough and was an alcoholic. In the film Darling you get a glimpse of what she was capable of and what she might have achieved had her life and luck have been different.