What is her definition of "modernist" pattern?
There are so many different takes on modern, that what it is for one person,
is not at all what another considers modern.
You might want to check first, rather than risk her being disappointed.
Agree, a dresden plate may work, however that is a very old traditional pattern. (in my mind)
You could super-size any star pattern (or any block for that matter),
to one block for the whole pillow, as often seen in modern style quilts.
Then quilt it with all straight line quilting. Again a style of quilting often in modern style quilts.
You could do them identical ... or a different block for each pillow.
Then they'd be alike, but unique for each pillow.