Somebody who's become a germophobe, agoraphobe, hoarder, and just plain batshit crazy, that's what it looks like. And an elderly spouse who no doubt loves her but is ill-equipped to handle the real-world consequences of all that, especially now that there's, like, more than a quarter-million dollars on the table.
The authorities will be called in before this is all over, my money's on that, and then god knows what happens, elderly abuse, criminal insanity, just insanity period, god only knows what. I don't think any of us can attiribute "motive", but the reality appears to be pretty stark at this point.