Well, I said I'd update you on this but it's taken a long time!
I finally found my Pandora picture by dragging the image into Google Image search. This dainty little soul is from a painting by William Henry Margetson. The print is on silk and I've found a couple of sites with her for sale, but there isn't much about this particular painting. Called variously The Iron Chest and Girl With a Treasure Chest it was painted in 1924. Oxford Art Online gives the artist a scant few sentences, but tells me that he lived from 1861-1940. There is however a brief blog post here which has a good range of his images, all of a similar style. There are also collections of his work on Pinterest. It looks as though he was a populist painter of delicate ladies in various situations, but also did a number of illustrations for fairy tales, poetry, biblical stories and adventures with delightful titles like "The Tyger of Mysore" or "With Cochrane the Dauntless". He seems to be a rather derivative artist, I can see parallels with a range of painters from Waterhouse to Kroyer, perhaps the reason Oxford are a bit sniffy about him!
I still think she's lovely, even if she isn't Pandora!