Perhaps you should get tested for food allergies/intolerances if you have concerns. I went GF/CF recently, and noticed a huge change all at once...but then I put dairy back in my diet and there was no change. I'm still gluten free, but after a few weeks it became obvious to me that there's no reason for me to continue avoiding dairy if it has no negative effect on my health.
I should also point out that I had some pretty bad health problems as a result of my gluten intolerance. It triggered my hypothyroidism, which caused me to gain weight, made me anemic, and made my cholesterol levels really high. I had no real issues with casein that I know of (though I still generally avoid cheese because it's pretty bad for me anyway).
So while it may have an effect, it's gonna be a biological one before a brain chemistry one, and it may be more of a placebo for your mom than an actual help. If you don't mind needles, maybe you could request a blood test? Even if you don't take a test, if there's no obvious change, point that out. Eating GF/CF is a real pain, especially if you're with friends....