I think the very fact that the only thing that's really missing is the alcohol shows that the reason she fled was because she just didn't want to get caught driving with all that alcohol, some of it being opened. I don't even know that she was necessarily all that intoxicated. She may have been but either way she'd need to ditch the alcohol. I have always thought that she trusted the wrong person, or the wrong person got a hold of her. I do think she was still alive for the call to her bf's cell. But I think by 2 days later her cell would have been dead so she would have had to use a landline. Maybe a perp stopped at a truck stop and she told him she had to use the bathroom. Maybe she was able to get to a pay phone.
I wonder if she left her phone charger in the car. If I recall correctly, the call to the bf's phone was about 2 days after the car accident. Perhaps, she was staying with someone?