Remember how I talked about Ema and her fancy snap-on feet that are incompatible with the Lucznik's old sturdy ones?
Well, in aunt's box of tools, there were also two sewing machine feet. Including a rolled hem foot.
And it fits!
It's obviously not a fancy snap-on one, but it fits.
(Also, since I wrote that post about Ema, I found a stash of empty bobbins - I'm even more grateful now that they're interchangeable!)