Need some insight...should I pay off mom's car or get a new car?

You've done OK so far having your own car with no strings attached, so buy another new car- all your own. If your mom wants to spend $1000/month on rental cars, she needs to trade in her Camry on a Sienna and feel what she likes to feel in a bigger vehicle. Maybe she can work it all out without complicating your life. She has so much money for rentals, she can pay off her Camry if she wants to.