My condolences for losing her so early.
My mom hit 87 in June and even after a stroke in May she's still sharp enough to run the family properties but she's so weak and blind she had me take over day-to-day management and finances while she sets the policy.
I'm not sure which is the worst way to go, sharp mind and failing body or mind failing first. Both her remaining older sisters (she grew up as one of fourteen kids, only two left now) didn't know who or where they were at their end recently and I think that really scares her.
