Minnie's fabric has not worn well, it is very thin and there is no colour left. The pale orange blotches in the photo are the backing fabric showing through the block. Sometimes the seams of the patches still show some colour but I don't see any in this one. All we have is the piecing.
I have also been unable to find a name for this block. It looks familiar but nothing matches.
I have pieced the design as two colours and as three colours.
I'm interested in your interpretations.
A - 2 light and 2 dark 2" x 2" squares.
B - 2 light and 2 dark 2.5" x 2.5" squares. Cut diagonally to make 4 dark and 4 light triangles.
C - 1 light and 1 dark 4" x 4" square. Cut diagonally to make 2 light and 2 dark triangles.
Add two B's to square A; sew to C. Trim to 3.5 inch square.
Block measures 6.5 inch square.
This following block is called Four Knaves from Nancy Cabot in 1938; almost the same as Nellie's Mystery.
A - 6 purple and 2 green squares 2.5" x 2.5". Cut diagonally to make 12 purple and 4 green triangles. Make four half square triangles and trim to 2" square, add two more triangles.
B - 2 green squares 4" x 4". Cut diagonally to make 4 triangles.
Block measures 6.5 inch square.
Make one of each block for your mystery quilt. There is one more block to come, then all will be revealed!