Sorry to hear about your wife’s vision problems.
As others have said, there is unfortunately no way to increase the font size. I’ve seen many complaints about this and there’s not a small number of people who think the UI designers were stoned when they came up with the latest version of the UI but either way there’s not a great solution right now.
As others have pointed out, you can purchase things like the S3XY buttons or an auxiliary dashboard to help, but those don’t fix the fact that fundamentally the car is a poor fit for your wife.
Are there other cars with which she would do better, or do her difficulties apply to most/all cars? If it’s not an option for you to drive the Tesla and for her to drive your current car I think selling it would be the best route.
As far as how to sell it, you can check on trading it in for the car she chooses to replace it, sell it online privately or sell it to a reseller like carvana.
The UI designers are young with young eyes, and they are for the most part Apple users who think customization is the devil.