There were a LOT more dirt/gravel roads and parking lots.
Driving on roads in the rain could be dangerous too. Roads only had a line in the middle. Nothing on the sides.
Also, nowadays a yellow dashed line in the middle of the road means two way traffic. White means both lanes go in the same direction (like on freeways/tollways). In the 50's they were all white.
This is one of the things I have noticed in some low budget movies and tv shows. They are supposed to take place sometime before 1970, but the roads are painted/striped as they are today.
Also, roads didn't have the nice shoulders they do today.
She needs to be using drum brakes, bias ply tires, and leaded gas for sure. Although she would get "full service" when she stopped to fuel up - and maybe even a free bar of soap or green stamps with her fuel purchase.
She could visit McDonalds though - if they would sell burgers for 15 cents and fries for a dime.
Not to mention the changes in grade for some roads. I think there is a section of Rt 66 in New Mexico (La Bajada) where the cars had to go up backwards because they didn't have fuel pumps and the cars would stall when their gravity-fed carbs became starved for fuel.