I would tell Tony to ignore her. At the most, have him write her an excruciatingly polite letter explaining that he had mentioned his grandmother to the reporter, and it is not his (Tony's) fault that because of the writing and editing process, she didn't get mentioned in the article. He should "thank" her for her ineterst in his article, and leave it at that.

You cannot choose your relatives, but you can choose how you react to, or deal with them. It seems that putting this one at a distance - formal-sounding letters only, if anything - would be the better part of valor. She's not worth the energy or effort that getting angry entails.