And honestly, I have to comment - if you are just getting back into riding after a long time off with rusty skills, I think it's going to be important to send her to a trainer eventually. Doesn't mean you have to go out and be involved with the wider horse world if you don't want to, just educate your mare so she's a solid citizen.
As a father, you wouldn't let your kids not go to school, would you? Because eventually, they're going to leave the nest and need the skills they'll learn in the wider world to take care of themselves, and achieve success.
Horses are a lot the same way - they live a long time, and we can't promise them forever. Eventually, things change. Health problems, injuries, job losses, economic ups and downs, etc. Something is bound to change over the next 20+ years of this mare's life, and you may have to part ways with her, even if you don't want to, or don't think it will happen.
Making sure both she and you have a good, well-practiced skill set are the best ways of ensuring that you have a long, safe, and fun life of riding together :)