Is it impossible that dehydration caused this?
Except that we know from the autopsy that she was blind, because her visual cortex was destroyed
Is it impossible that dehydration caused this?
A good question, but it couldn't been caused by the dehydration. The autopsy report says: "Of particular importance was the hypoxic damage [damage caused by lack of oxygen] and neuronal loss [the nerve cells were gone] in her occiptal lobes [where important visual centers are located] which indicates cortical blindness."
A quick translation: the lack of oxygen led to the death of the nerves in the part of the brain that "processes" vision. The only time she was known to be without oxygen was during the original cardiac arrest the night she collapsed.