a beginner could make sashing out of any long narrow woven or knitted stuff, as long as the shrinkage rate is the same as the rest. in this case, everything was prewashed, so the sashings should also be. but the sashing could be any pretty ribbon or decorative trim that matches the quilt top. creating a sashing out of fabric and sewing it to the quilt top, matching raw edges with 1/4" seams, and ironing over the rest of the tube, and then stitching that down in place, may be more effort than the original quilt was to have been. when i see the original quilt, i see that a simple pattern was chosen. the sashing method described is much more difficult for a beginner than the quilt. using a premade sashing of some kind, i think kwhites idea of straddling the squares is great.
i agree with the rest of you that too many 'lessons' in one project may be too much for beginner. walk before you run, right?