My friend D.W. suggested simply that during the sulfur, fire, sand and salt storm, Lot’s wife was completely covered in salt, her body forming into what looked like a pillar of salt. Since pillars (i.e. concrete buildings) are often described by their exterior (concrete) and not their interior (office space), so too in this case. Her body did not become salt, she was simply covered with it.
Obviously, being covered with salt, she must have died quickly. What happened afterwards I don’t know, but it’s reasonable to assume that the pillar disintegrated over a short period of time (my guess is a few weeks, mayber a bit more,salt is a preservative) and since then has been unidentifiable.
A rational explanation that fits neatly into the pasuk. Take it or leave it. I take it.