I read on a separate facebook page (back in December-2017) a theory about Diane displaying behavior consistent with carbon monoxide poisoning (exposure either from the campsite propane tank or from her own vehicle). This would include the severe headache, impaired vision, dizziness, confusion, and irrational behavior.
There were issues with Ford Explorers in recent years where police officers were getting carbon monoxide poisoning from exhaust being recirculated back into the vehicle from the dashboard. Diane drove a 2003 Ford Windstar, in which that particular year, make, and model has one of the highest consumer complaints of all versions of the Windstar. I can't source any CO poisoning complaints for the Windstar, but the person who was sharing this information supposedly found some consumer complaints for the 2003 Ford Windstar which included CO coming into the vehicle.