I was just coming to post the same thought. And to repeat what so many have said--I just can't see why anyone, in a panic or not in a panic would purposefully stop-at a stop sign in broad daylight in a residential area-to dump a body.
One thought could be "taunting" by the killer, but honestly, I've only ever seen that level of taunting in the movies.
IMO, the body fell out of whatever vehicle she was in. Car? Door not closed? Truck? More likely, IMO.
Or, less likely, someone else opened the door and pushed the body out. Just throwing spaghetti here.
Where was the vehicle headed? If there was an actual destination, there may be more clues there. The dump? The lake? Retaining pond? Maybe evidence thrown out window on the way?