Maybe so. Maybe just because the location in which he encountered her (plus her smaller stature) made it convenient to hide the body, whereas that wasn't the case with the other two? (I don't know the layout of the neighborhood so it's just a guess). Maybe (and possibly in combination with the above)because she was the furthest away from where he lived, and he hid her so he had more time to get away. It's a great question, and there are many possibilities.