That's what I've thought for awhile now. Whoever is driving Tammy around is using that van. Plus at least half of the back passenger seat has been removed to accommodate her. Whether it's Michael, Chris, Tisa, or one of the sisters driving, with a camera strategically mounted in/on the front passenger seat, if that van is on the move then Tammy's on the rear floor. Even Rob had to take that van to drive Tammy home. When Michael has had to race Amy to ER previous seasons or their little babymoon vacation, they've switched to a standard sedan. When they went on the family vacation Michael and Amy had to rent the second van.
Speaking of the family vacation, it would be interesting to know how much extra the siblings paid just so they could include Tammy. The extra van rental, the trailer rental, the wheelchair rental plus ramps. Then it cost them extra to rent that motel room for her...and eventually they had the cost of Rob renting a car to come and pick Tammy up, which was left with the family as he had to take the van to get Tammy home. It's ludicrous the amount they put themselves put for such an ungrateful sibling...and yet Tammy can frame it in her own mind that everyone else should be grateful that they don't have to do more. I hope we get a good idea next episode of how long Tammy manages to remain at home after Amy and Michael leave before the current inpatient/nursing home saga begins.