Genesis 19:24-26 Then the Lord rained on Sodom and Gomorrah sulfur and fire from the Lord out of heaven. And he overthrew those cities, and all the valley, and all the inhabitants of the cities, and what grew on the ground. But Lot's wife, behind him, looked back, and she became a pillar of salt.

This seems like a rather harsh punishment for simply looking back on Sodom, which was formerly her home.  Did she really deserve to die for this? Why did god choose a pillar of salt? Why not a tree, or a rock, or simply just kill her?