I totally get your concern OP! I’m 62 and doing as much as I can to keep fit and healthy.
Myself and quite a few friends all retired at just over 60 and just a couple have aged really really quickly. As you say, their world has become smaller, they stay at home, read, watch TV but almost withdraw from the world and their health is already suffering.
I would suggest a couple of things, see if you can get her to go for a thorough health check, eyes, ears, thyroid, bone density. Thyroid issues go undiagnosed in many women because so many symptoms are similar to menopause. As other have said, sight and hearing issues can cause problems with driving, especially at night.
Then, she needs some structure to her week. She doesn’t need to be out every day, but she needs some out of home activities.
I took up adult ballet at 62, I’m terrible, but it works my brain and my body. With all the terms in French and remembering everything, I find it a solid hour of brain power being engaged. Another day I meet friends for a walk and coffee. Coffee generally take us at least 3 hours. Another day I go to a gentle Zumba class and one night a week, Pilates. I’ve recently found out my bone density isn’t good, so I’ll be adding some sort of gentle strength training next. I’ve also found all classes where I can pay weekly, with no full term commitment. So if we want to go away or change plans with little notice I can.
See if she can think of something she enjoyed as a child and gave up that she can begin again, or something completely new. Something just for fun, something for fitness and something which gives her a social connection.
I want to be the 80 or 90 year old still giving life a good go if I can. I’ve retired from work, but not given up on life. Your mum is still so young. It’s far too early to be shrinking her world. I totally understand your concern.