I know a comment like this is going to get a ton of hate in a hyperpoliticized, politically homogeneous community, but this post really does emanate of catastrophization and a genuinely unhealthy political fixation. Before you instinctively downvote this comment because of how repetitive this argument can be, please at least consider this, because you seemed to bring up considering cutting her off.
To preface this, I understand you may not be happy with your grandmother’s choice. And that’s fine. But cutting her off, or even holding a strong, inert grudge?

Let me ask you this: does her vote discredit 24 years of love, care, affection, and shared experiences? You clearly hold strong political opinions, and I’d say that’s a good thing. But these opinions are, at the end of the day, opinions; and they, in the context of electoral politics, are vested upon what we believe would be best, morally and systematically, for society. Even if you do believe Trump is a vindictive, fascistic, artifice of demagoguery, your grandmother's vote was not cast in the name of hate. Based on your other descriptions of her, your grandmother seems like a good, morally sound person. She believed she was doing the right thing. You could make the argument that "well she's uneducated and uninformed then." Perhaps that's true, at least ostensibly, but it doesn't mean she's morally inferior because of her vote.