I was just going to say this! My MIL passed away a few months ago. She was 83; a widow since 2017; still lived independently in the home she and her husband built 50+ years ago; drove somewhere several times a week (she lived in the middle of nowhere so it was a 5-10 mile drive to get to her doctors, grocery store, etc. so it wasn't like she was just driving a few blocks); and still volunteered at several places. Her death was sudden and unexpected (massive heart attack about an hour after returning home from a social event). At the funeral, we had *several* people mention that her driving the last 6+ months had been bad. Her friends said they had stopped letting her drive them anywhere several months before her death. They said she just wasn't alert enough and would run red lights, pull out in front of people, and often drift across the center line. Now, we have no idea why these friends didn't mention this to any of her kids. She lived in a very small town where everyone knows everyone and they definitely knew how to get in touch with at least 3 of the kids. She had children living 2, 5, and 10 miles away from her, and someone checked in with her by phone/text or in person every day. Yet none of them ever thought about having her drive them anywhere to make sure her driving skills were still at a safe level. We were all really thankful that she didn't cause an accident at any time and that her heart attack happened while she was in her home and not while she was driving.
So, OP, my suggestion is that before your mom leases or purchases a car, either you or your sister should pay her a visit and figure out an inconspicuous way to have her drive you somewhere while you're there. Another thing to consider is if her (hopefully) future move has her moving to another state, she might have to provide medical documentation that she is still capable of driving (it varies by state) before getting her driver's license in that state. Would a doctor support her continuing to drive? I know it's really tough to have this type of a conversation with an aging parent, but it really does need to happen. My siblings and I had to do this with my mom when she was in her early 80's. She didn't want to give up driving. We didn't think she should be driving at all (she had several health issues) but she didn't agree. We compromised (short of taking her keys) and said she could drive to the grocery store and drug store (both just a few blocks away and all on streets that were 35 mph or lower -- most were 25 mph) but one of us would drive her to any doctor appointments as her doctors were all 5-8 miles away and required highway driving. She was fine with that, but after a few months (and 4 months before she passed away) she said she didn't think she should be driving at all and gave her keys to my sister. We're sure *something* happened that made her change her mind. There were no dents or scratches on the car so it was either a near miss or maybe a situation where she couldn't remember where she was going or how to get there. Whatever it was, we're thankful no one else was involved.