I'm not sure this action has much meaning, for me personally. Also, when speculating on the person walking around to check the passenger side door, what does that mean? Does that mean they tried the door handle but the door was locked, just peeked in the window, etc.? I need more information (yet again, ha) to give meaning to this action. For instance, I drive a new vehicle and I go around to the passenger side all the time to retrieve items rather than dragging them across the console into the driver's seat. Sometimes I'm distracted with kids, phone, randomness, and I lock the car on autopilot and then remember my purse, or other items. I usually don't realize it's already locked until I lift the handle and it the door won't open. I'm not checking to make sure the car is locked even though it might seem that way to someone glancing in my direction. It's hard to say, but for me, this issue doesn't sway me one way or the other regarding the identity of the woman.
~Let's say it was Erin: I'm not saying the hunting story is true, I'm just speculating that if she thought she was going hunting in the desert, she would most likely have prepared a daypack with water, sunscreen, food, etc. She might have placed it on the front passenger side seat, back seat on either side, or in the trunk. It's hard to say without knowing her usual habit. Let's say she had a pack and placed it in the front on the passenger seat, I would think the pack would be easier to gather from the the passenger side rather than dragging it across to the drivers side before getting out.
~Let's say it was NL: I'm sure she would want to wipe the passenger side door handle off before abandoning the car. She would want to erase any evidence that she, or CL, were ever in that car. Or maybe she saw the car driving by and she was already out of Erin's car and she was afraid to draw attention to herself. In that case she might have walked around to the passenger side to give the impression that she was fine, but having car trouble and she was looking at damage or checking things before she left in the other car. She resembled Erin and leaving a disabled car to retrieve later is far less suspicious than someone abandoning a working car in the middle of nowhere for no reason. Another scenario is the same as above. Items were left on the passenger side and she went around the car to retrieve them rather than pull them across.
Yet again, who knows?