I was just thinking, if your mil still has remnants of the threads and fabric she used in the quilts, you could create several samples to test for colorfastness. I would just machine stitch the embroidery threads onto the background fabric. If there is enough, I would cut this up into several test samples and submerge one in water to see what happens. If there is no bleeding, you wouldn't even need the other samples. If there is bleeding, you could try washing a sample in hot water and Synthrapol, etc.