LOL the interesting part is, the google maps gives you the option to move the blue line which is the route and it remaps an alternative route. If she saw the highway and knew that she was not allowed to walk there as a pedestrian, she could have looked at the map and looked for a safer road, moved the blue line on to that road and then it would remap a new route to where she wants to go.
Even if she had no clue how to use it to begin with, I can't see her using this as an excuse to be walking down the highway when clearly it is not legal to do so. So if the direction tell her to jump of a clif, she would have done so as well?