The two points can be made into a right triangle with the two sides defined by two lines drawn from the two given points. Use the Pythagorean Theorem to solve for the hypotenuse, the distance between the two points. See attached graph.
Everytime the curve climbs, it means Sue is travelling. Everytime the curve stays flat, it means Sue is stays stationary. It remains to count up the total for both categories, with one square being 30 minutes.