Last Sunday, my grandmother was supposed to meet a friend for lunch. Instead of meeting her friend, she thought she was coming home from work and decided to blow off her friend and somehow got lost. She was missing for almost 10 hours. Grandma's friend kept calling my grandmother's house phone. My aunt heard the phone ringing but was under strict instructions from my grandmother of not to touch her phone. It wasn't until the friend called my aunt and talked to her, she realized that she needed to call the police. It was hours later but the police were able to locate her and bring her home. My aunt sent a copy of the police report to my grandmother's doctor and my mother had a long talk with the doctor too. Grandma has an appointment with her doctor on the 11th and she can't really fool the doctor at this point. The next time she gets lost, she might not get so lucky. We know grandma shouldn't be driving, but we are hoping that the doctor will help out with giving up the car keys.
My GFs father actually did lose his keys and licence and the pants they were in. Her Mom looked everywhere but couldn't find them. He suffered from ALZ. Her Mom told him he couldn't drive without his license. He agreed and let her drive. Yes, his stuff was found under the mattress on his bed. By that time he never questioned about driving.
I can't imagine very many things equal to compromising someone's mobility, and arranging to have her license suspended. Use the Indiana Jones trick: find a replacement first.
You and other close relatives (I'm assuming from your post that your aunt is also close) can discuss it privately and work out who will take Grandma to different appointments. Even if you're not interested in staying with her, you or the driver can shop or find something safe to do. Sometimes I'd visit the local library. Even in a pandemic, there are still places that aren't really close to others once you're inside the library.
Then after Grandma has finished her trips, take her someplace special. If we weren't in a pandemic, I'd suggest a restaurant. But perhaps you could pre-order then just stop by to pick up the meal, take it home, and let Grandma tell you about her day.
We live in a county with a lot of lakes, so I would take Dad for a drive by the ones which had large numbers of swans, and we'd watch them for a while before getting our DairyQueen or going out to dinner (this was before the pandemic.)
You can also buy flowers and give them to her. If you (a) make her feel special and (b) pre-plan so she doesn't panic and feel as though she has no transportation for necessary or social occasions, she won't panic as much, or she might find that she enjoys having a chauffeur.
Needless to say, her phone should be answered when it rings. Like BurntCaregiver said, allowing a demented elder to call the shots anymore is totally illogical.
Wishing you the best of luck with a difficult situation. I hate dementia with every ounce of my being; my mother is 95 this month with advanced dementia and falls on almost a daily basis now; that's how bad things have gotten. She simply does not remember she can't walk, so she tries to get up and falls. God help these elders and all of us who are walking this path with them.
Granted everyone is going to catch a lot of hell but everyone will just have to suck it up for a while. It's going to be tough going but not forever.
Your aunt also has to stop obeying her orders at once. Aunt is a grown woman and not under strict instructions from a demented senior not in their right mind to not touch the phone. That has to stop today. For your grandmother's safety and everyone else's as well.
Your grandmother may very well be able to pass a cognition test from her doctor. Some seniors are so good at showtiming that they are able to put it over on their doctor. Your grandmother's doctor has already been given a heads up ahead of time with the police report. He can't take away her license or even suspend it temporarily. The Department of Motor Vehicles has to do that and they will. The doctor will have to send them a copy of his results along with the police report.
In the meantime, no one lets her drive. She's going to make everyone's life a living hell, but the family has to do what must be done.
Good luck and you'll see everything will work out for the best.