Nothing much to disagree with here. You can't take it with you, and since its probable the author of the Q has no direct children (if they are part of the story then it doesn't alter things much) the outcome when they die and no longer 'care' is going to be .. interesting.

If they don't consciously alienate their family in a will which is legally threat-proof, then the sister who they dislike may well come into a windfall.

Making the will is going to incur thinking about what to do with the money, which she can't contest in law. Probably, give her some non-tokenistic small amount (I mean like not 5c) and then remove her basis to complain. out of 55mil, one might do it.

I like how the A side of the Q/A said "give it to elder abuse charity" which goes directly to the personal complaint of Q in this. Nice play.

I think we've all wondered how well we'd cope with a windfall. I think this is as good as many, and a lot less bad than many, and maybe, not telling was the wisest course.

(I have known people 2-3 orders of decimal magnitude richer than me, and by and large as long as you accept the fundamentals across the canyon its ok. The ones who are less than one decimal order of magnitude can get a bit fraught because you really can do turn-about for shared experiences but you can't get the bottle of petrus they did, nor should you even try)