The replacement for the Heir Presumptive would need a great deal of information about her. One likely source would be the palace surveillance videos, probably from Roger Lang. I found no indication that Roger Lang was periodically sending packages - either he was not the source, the surveillance videos were not being used this way, or he passed them on in a different manner. Again, the current investigation is better placed for, and has the resources for, examining the surveillance videos which cover the areas in which those records are created and stored.
The most productive lead is probably the result of examining the car from which the Heir Presumptive was abducted. On the loop road, near exit 16a, the driver gassed her. About fifteen minutes later, the car stopped, a couple people pulled the door open, removed the Heir Presumptive, and the duplicate got it. The car pulled away.
The investigation has traced the car's path a little further than exit 16a. Based on that, there are too many likely locations. A park (which would require turning around), a car wash with an isolated rear area, six office park parking lots (two of which would require turning around), an underground parking garage (unlikely, too dark), and many residential houses with garages. Four of those houses are shuttered and closed, and warrant further investigation.
At this point, enough time has passed that I am convinced Donella is not in the city.