We know that the faster she climbs, the less time the climb will take.
As you can observe, the given relationship is between her speed and the height of the climb. We can deduct that this situation can be modeled by the speed in function of the time.
However, let's analyze each answer choice.
Choice A can't be right because the height of the mountain is not variable, that is, the mountain won't change its height.
Choice B is relating time and speed which, as we said before, the situation involves a relationship between time and speed.
Therefore, the right answer is B.