To me I care because it MIGHT lead to knowing if something happened BEFORE they got to the house. Did she move to the back where someone tried to take advantage of her and she struggled and died? Did someone PULL her into the back. Were there really two people in the back like mom said and two upfront? Was one of those dropped off and another witness? Yes, speculation, but isn't that what we are trying to do here? Speculate to help better understand what happened?
Let's say they killed her in the car and went to the house to figure out what to do. That leaves 5 hours to dispose of her body, a lot of time and a LOT of area to cover! If she made it to the house, partied, died while they slept and they woke up at say, 7:30AM and had maybe an hour to dispose of her body, a ton of time and area difference there.