Margaret Watts, the daughter of the illustrator Arthur Watts, was a neighbor of Gluck’s in Hampstead. Gluck painted Watts aged 21 as a fashionable young woman; she later became a costume designer. (https://www.nytimes.com/slideshow/2017/02/01/t-magazine/art/a-groundbreaking-20th-century-artist-rediscovered/s/01tmag-gluck-slide-AGXE.html)