Somebody read to me from a book about Allingham long ago that she would "polish her prose until it shone over-bright" and then dictate it to her husband to reduce it to a more readable vernacular. I think it was a line from a biography describing an interview with surviving relatives. I've repeated this line many times, and then recently went to track down its source again--and I can't.
What I did find was this line by Allingham herself:
I write every paragraph four times - once to get my meaning down, once to put in anything I have left out, once to take out anything that seems unnecessary, and once to make the whole thing sound as if I had only just thought of it.
Which has the gist of the quote I remember, but doesn't mention dictating to her husband, is in her own voice rather than a third party, and doesn't use the phrase "shone over-bright," which I remember quite clearly.
So, where did that description of her writing process come from?