Maybe if you insist to her that she get her son tested ASAP, and she discovers he's not so highly gifted, she'll drop this as a hobby? And since you no longer have this in common, she will go away.

Will your mutual friend be upset with you if you were to very gently explain to the crazy woman that you have nothing left to offer her, and she should consult online resources such as Davidson and Hoagies for any further needs she might have?

Sorry for the run-on sentences, it's 1:30 am.