A big part of me thinks the car is the key. Not that someone wanted the car but someone could use DNV just buying a car as a way to make folks think she got her new car and drove off in the sunset. But it would have to be someone that knew where she was that evening. So because of that maybe random but if it was someone random following her from the Dublin why would they take her car. I would think they would take her and leave the car.
It's quite a coincidence that on the day that Danni bought a car, she vanished after pulling over at the Shell station to search for her missing phone. I agree that the timing would suggest that Danni voluntarily disappeared, and that whomever is responsible had to have personal knowledge about Danni and her plans that evening. If Danni had not forgotten her phone at the Dublin, we probably would not be discussing her disappearance.