At first glance I was sure that it was a Dresden Plate (without the folded ends to create the points), but after looking at it a little more it does look like an "un-kaleidoscoped" kaleidoscope block. For a while I thought kaleidoscopes were a fairly new technique, I've learned differently...it's possible your grandmother could have called it something else though. It kind of looks like a 'buggy wheel' block or whatever that's called too. :) Thanks for sharing!