Crawlspace versus Slab. I like the way a raised floor looks and feels, but what about settling?

The piers in your Grandmothers home are probably not supported properly. This will allow them to sink. The floor joists may also be undersized to hold the load of the floor surface. Crawl space homes have many good points over slabs. The plumbing can be accessed and the floors will not cause back problems are just two.