To drive a rental that is rented by some one else you have to be a listed driver. So unless you are a listed driver you cannot drive the car legally. If you do drive and not listed and have an accident, well good luck as you will need it for the trouble every one will be in.

Mr. Jason, why are you asking here? We have no clue as to the policies and terms of auto rental companies. If you failed to consider asking a car rental company directly and went for the smartphone then I must advise you not to do that. Please always think issues completely. No matter what anyone says here it has zero bearing as to what any auto rental company may say. This is resolved by picking up the phone and calling an auto rental company in Oklahoma. You are welcome.

Nice idea, but YOU aren't old enough to drive a rental car.

then she will be the only one that can drive it

you can't