Just to kind of echo what others have said, most likely this was a two-person stalker job. I hate to sound like I'm stereotyping, but anyone who knows the area knows that there's no scene more common than two guys driving around in a pick up truck. I say it's probably a stalking case gone violent because the perps knew exactly where to find her, where to put her car to make people think she was in that area. I'm guessing she might have been followed from her house.
Your entire post was great, but I snipped this part to elaborate. I wonder if she wasn't involved with or talking to someone else's boyfriend and this became a 'prove your love for me' kind of plotted revenge. Or, perhaps she was talking to a white boy, and his white girlfriend/parents didn't like it very much.
Yeah, I know it sounds over the top, but lately we've seen some weird conspiracies over some fairly petty things. Especially amongst young people, who don't seem to know how to control their emotions like they did in times past (adults don't either, FWIW). Their rage over minor things can be mindblowing at times.