After my daughter tried it on a variety of dolls (it fit precisely none), I embarked on a little search to see what I could find out about it. Almost right away, I discovered it again on eBay, in its exact opposite color scheme of green and white:
This second pamphlet has a subtitle that reads: "For Kitchen Pick-Me-Ups." So, not just my mother-in-law's ancestor, it seems, but a whole bunch of other people's ancestors, crocheted little figural pot holders—not just in the shape of doll clothes, but also bird cages, animals & insects, fruits, wagon wheels, snowmen—to decorate their kitchens. Which also explains why our "bloomers" are a bit on the thin and not-quite-heat-resistant side. And I'm starting to wonder, now, if somewhere out there exists an enormous stash of these things-I-had-never-before-heard-of, waiting to be unboxed and to brighten a new era of rooms. But I've only found a few online here and there, and none are quite so lovely as the white-and-green bloomers hailing from the McGuiness family; or the reverse-color green-and-white ones abandoned to eBay.
There is one more thing I know about these bloomers. Their pattern is spider lace and blocks—spider lace showing up, in my very scant research, in US and UK patterns books from the 1910s onward. It consists of a series of chain-stitch rows that are then stitched to each other, and you can find a tutorial on how to do it here.
Meanwhile, if you know anything about the history of figural pot holders, write in and let me know! Have an heirloom you'd like to share? Write in with that, too. Next up, I'll be plundering the mysterious embroidered pocket full of hand-edged handkerchiefs, from my own side of the family.