OP: Do you know yet which company you will be renting from? Some companies, such as Hertz, automatically let a spouse drive without additional charge on rentals in every state if the renter is a member of the company's frequent-renter program.

https://www.hertz.com/rentacar/reser...ATORS&EOAG=ORD

That would obviate the need to worry about differing state laws on this issue.

Even without frequent-renter membership, some companies always permit spouses to drive for free on U.S. rentals:

https://www.avis.com/en/help/usa-faqs/additional-driver

https://www.budget.com/en/help/usa-f...-driver-policy