Crash investigators do this for a living?

Yep agree, unmarked road without any warning signs is a cause for a lawsuit regardless if a belt was worn or not. Still if she was wearing a belt and still ejected from the car anyways, there will be signs of this. The most obvious being a belt width bruise or contusion across her shoulder area, as well as the belt mounting points on that seat belt being bent inside the car from the force against them, and belt retracter pendulum brackets being bent from locking down and holding the belt tight.

This brings up another question. If she was wearing her belt and stiil was ejected from the car, how did that happen? Did the belt fail during the wreck causing this? If so, you may have grounds for a lawsuit against the car company too.