But I wonder if repeating a hill of the same grade multiple times is enough preparation for a longer of similar hill in a race situation.
That's essentially the idea behind certain kinds of speedwork. We run multiple repeats of a distance shorter than goal race distance at goal race pace, sometimes faster, sometimes slower, depending on the goal of the workout.
I think her plan sounds like a good one. Just don't forget to carefully work on the downhills also if she will experience downhills in this marathon.