But, to this point, I have only come across a single photographic image of her.
The image, shown here, is from Page 187 of "Third Book of Junior Authors" which was edited by Doris De Montreville and Donna Hill and published by the H.W. Wilson Company in 1972.
That's it. Just a black-and-white, slightly grainy side portrait. There's no way, even, to know what decade it's from.
Online image searches net nothing but covers and illustrations from her many books of folktales.1 No photos of Manning-Sanders herself.
Somewhere, I hope and suspect, there is a British library or Manning-Sanders descendant with photos of Manning-Sanders. I hope they surface some day. For the sake of history, we need a face to associate with this woman, who was one of the greatest and most important collectors of fairy tales in the modern era.
1. Many of those books were illustrated by Robin Jacques. Images of his illustrations are plentiful and instantly recognizable.