MSG isn't derived from corn, and even if the sugar that fed the yeast that made the glutamate came from corn, by the time it's commercially sold MSG it is so chemically pure that it would be irrelevant.
According to Wikipedia, it is made from starch, sugar beets, sugar cane, and molasses.
And starch quite often is corn starch.
As for the chemically pure aspect, I don't know enough to comment. No one really understands what causes allergies and no one can point out what aspect of corn causes it. For example, she also has a milk allergy (not intolerance), but does not have issues with milk that has been cooked, such as creme anglaise for making ice cream. Something with cooking the milk changes it. As for how this is related to corn, who knows. What part of corn caused the allergy? If you don't know, how do you know it was removed in the process of making MSG?
