Short term lease?
Investigate whether she can negotiate with a taxi company for a monthly rate.
Often they'll put the passenger with the same driver, sort of an on-call system.
The passenger/driver camaraderie develops, a more comfortable situation for her. And she doesn't have to worry about paying each trip, how much a particular trip will cost, etc.
Another possibility, my city has Links Paratransit, and maybe Las Vegas has something similar. Your aunt would submit an application, signed by an MD "or other medical professional". Once approved, they'll transport her just about anywhere space permitting, door to door. Here the cost is like $1.60 per person one way regardless of milage (though that may be limited). Once she is in their system, she can call and schedule rides to go shopping, church, doctor appt., etc. They usually ask to be called a few days in advance, but again, once in the system they can be flexible when possible, space available. An elderly friend of mine used them once she gave up driving, and it was very satisfactory. Their vans have wheelchair lift, etc.
Good luck finding a solution.