My grandmother has flowers in her garden, and recently there has been a lot of white, squishy / soft bits in soil. I do not think they are perlites, as they are soft. My grandmother is convinced that as soon as they appear they ruin all the roots of the plants. Had a look online and cannot find anything! They look like perlite, but damage the roots.
These 'white bits' are vermiculite or perlite. They are added to potting soil to keep the soil from compaction. They have absolutely nothing to do with plants getting root rot if that is indeed what is happening. Are these plants in pots? Or did she dump potting soil on the ground to try to grow these plants? What else was in this potting soil? Water absorbers or fertilizer?
If she did dump potting soil on top of garden soil she's created a perched water table exacerbated by watering too much. That is all. Plants have to have drainage or the pores in the soil stay saturated too long and ta da, root rot. If we are looking at potting soil in pots, did she put rocks or gravel beneath the soil 'for drainage'? Again a perched water table. Let us know how often she waters, what the soil situation is (pots/garden indoor/outdoor) and what fertilizer she's using.
You HAVE to send pictures of the plants, the environment, the root rot as well, please! Also your zone, where you live, her maintenance habits...