Which route happened first? The van or the phone?
Random thoughts bothering me:
Did Jennifer leave the van in the parking lot as a meeting place to ride with someone else? I believe the van was somewhere else and someone else left the van in the parking lot. Why? Because of the keys in the van. If she were meeting someone, the keys would have been with her.
Did she meet someone, leave her van somewhere and rode with that person? If that is the case, and if that person was causing her fear...and say she pulled our her phone and they grabbed it and threw it out the window...that still leaves...where is Jennifer...and why would the person go back to her van and risk moving it ..or opening door and leaving keys in it?
If Jennifer had a near full tank of gas when she left, and told husband she was going to the mall, it would be expected that she would need gas used up in the van. This says to me...and with her "comfort level" that she would have been the most likely to have been the "driver" as opposed to getting into a different vehicle.
Did she pick someone up at their home? Did she meet someone in a public sort of place (parking lot) and they left their vehicle. She was the driver. Did something happen while she was driving and her phone thrown out the window? Did someone hold a gun to her to make her drive somewhere else? Did someone harm her and then drive her van back to their vehicle? Was their vehicle left in that apartment parking lot? Was their meeting place another parking lot and the person escaped and hopped into their own vehicle leaving behind the keys and van and someone else found it and took it joyriding and abandoned it at the apartments? Did she not meet anyone at all and maybe stopped for a soda or snack somewhere and was car jacked? (I kind of rule that out due to the rings in the jewelry box.) Why leave your wedding rings unless you are meeting someone?