The correct response is:
Her distance from the top of the waterslide is decreasing with respect to time.
As Isla walks up the steps to the top of the 125-foot waterslide, her distance from the top decreases continuously until she reaches the top. This means that the graph of her distance from the top versus time would show a downward slope that goes from 125 feet (at the bottom) to 0 feet (at the top).