> This is definitely not true. There is no biological pathway that can do this

Nevertheless, it continues to give her migraines even in small portions where other foods don't. I don't doubt it could be some byproduct from the process of MSG salt's synthesis or cooking with it rather than the actual glutamic acid, or some allergy as others have suggested.

I wouldn't be so strong as to categorically say that MSG can't cause migraines in any of the human race as you so claim though. There's so much we don't know about human biological mechanisms in niche cases; even water can cause allergic reactions in certain individuals (see Aquagenic Urticaria). What is true generally is not always true specifically when it comes to human health.

I'm curious: have you done a (single or double) blind test where you prepare dishes (selected at random) with or without MSG/aspartame/yeast extract and record the effects?

To be clear: not saying you should, just wondering how you came the conclusion that those ingredients are the trigger.