Am I considered a Mahram (unmarriageable relative) to my wife's maternal grandmother? May I shake hands with her or not?
Yes, you are a Mahram to your wife's maternal grandmother. It is permissible for you to shake hands with her and see of her what is lawful to see of your female Mahrams. (Part No. 17; Page No. 375) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.