I want to stand up for My/Your/Our account: as a child of divorce, I experienced how my mother was denied access to the joint account or the account was emptied, and she had little knowledge of financial matters during the divorce.
Therefore, my wife should definitely keep her own account; I see this as a contribution to freedom and individuality in the relationship. Also, I don't see every Esprit/Amazon/whatever charge, that would drive me crazy.
To the OP: as long as the current living situation with your grandma doesn't bother you, why change anything. You don't really have any hardship, but all the time in the world. And please don't give me any doomsday talk now. If it comes to the point where our money is worth nothing anymore, we might also have conditions that make the property owner jealous of the one who can still flee to another continent with his devalued few bucks.