I would like to clear up a perhaps possible misunderstanding on the fabrics from the 50's.
"Its just because of the kind of material that was available then, and possibly because the material was "worn" when she used it. I'm not sure."
The quality of fabrics available then were equal to or better than the quality we have now. It sounds as if your great-grandmother chose to use fabrics which had been taken from garments. These probably had sentimental value to her. Since they are thinner and you are having shadow problems, they sound as if they were dress weight. If they were from garments then you are probably looking at fabric from the 30's or 40's and men's shirts, women, and children's clothing. Depending on how old your great- grandmother was in the 50's and how she saved, the fabric might be even older. If she lived in a rural area or a small town then the fabric may be flour sacking as this was a major source of fabric in the early decades of the 20th century. If the fabric is only thin but without holes you may want to reinforce it with stabilizer as suggested to preserve the history of the quilt. If the quilt is a definite pattern and the fabric is color coordinated for the block selection then you can only assume your great-grandmother bought new material of her choice for the quilt top and the shadowing effect did not bother her, or else it bothered her so much that she decided not to finish the quilt.Old quilts provided a lot of interesting questions, don't they?