I think your second guess (standing doggy) above might be correct and the perspective is just really awkward (probably done so that you can see her face and the dick penetrating her at the same time). Each of her hooves are almost the size of her torso. The book at best makes them about as big as her head, so the proportions are off and I think this is just a case of the feet being foreshortened by being closer to the camera than the rest of her, and the part where the hooves "are above her head" is due to the angle you're looking from.
Quick sketch of what I mean: