She added corners to the 8" blocks,
rotating the sampler blocks so they are on point.
She used scrappy pieced corners all in this pattern.
You could also use a plain triangle.
The good thing about the math is that if you make the corners a bit large you can then trim the new blocks to a consistent size. No one (not even YOU) will notice that some sampler blocks are a little bit larger than others.
Getting out my blue card, my Fons and Porter's Quilters Need to Know Card (indispensible). I see that the 8" finished blocks will now have a finished line 11-3/8" across the middle. I figured out a pattern with a little to spare in EQ.
I'd cut squares 6-3/4" and slice in half for the triangles.
That will give you a finished square 11-3/4" (12-1/4" with seams). Then you can trim to a conisistent size, which would probably be 11-3/4". Make the triangles bigger if you want a finished 12" square.
Now adding that piecework pattern to the corners is a different thing. Too much for my math skills.
But didn't Terry do a lovely job?
Here's her photostream: