The French painting of the girl on the garden wall featured in last week's Middle Grade Gallery comes from The Saturdays by Elizabeth Enright (first published in 1941; Square Fish, 2008). The Saturdays is the first, and my favorite, of the books in The Melendy Quartet. There are four Melendy children, too (guess who is my favorite of them?), and in this book they decide to pool their allowances so each can have an Independent Saturday Afternoon Adventure.
On her Saturday, Randy visits an art gallery where French paintings are being shown for the benefit of war relief. That's where she finds the painting of The Princess, and its model, who turns out to be old family friend Mrs. Oliphant. The story behind the painting is long and best told as Mrs. Oliphant told it to Randy, over vanilla ice cream and petit fours. Suffice it to say that at one point Mrs. Oliphant is kidnapped by gypsies (I agree with Charlotte that this is a bit much).
Elizabeth Enright's own pen-and-ink drawings illustrate all four of the Melendy books. Here's one from The Saturdays of Randy in front of the painting in question (I scanned this image from my childhood copy). I'm still wondering whether Enright saw a similar exhibition in New York City and based her description on a real painting, or whether she made up exhibition, painting, or both. At any rate, we know what it looks like. Congratulations to Charlotte for recognizing it right away!