My theory is that someone (probably boyfriend) drove Abby to an NA meeting in Lumberton. According to na.org, they meet in Lumberton at Our Primary Purpose Building, 120 W 6th Street. They meet almost every day, also Tuesdays, at 12.00 PM. She left her house 11.30 AM.
Now the way to the NA meeting goes RIGHT THROUGH the area where three victims of most likely the same killer were found, and the area is a hot spot for drugs and stuff. This could be relevant but I don't think it is. She would often go through that area on the way to "downtown" Lumberton.
I'm not sure if police are allowed to say if her destination was an NA meeting, as they are anonymous, but that could be why they won't say anything about where she was dropped off even though they know.
She could have met someone at that meeting, and they could have made plans to go somewhere to do drugs or whatever. At that point she could have overdosed. Heroin addicts often OD when they do it again after a long break. And maybe that other person she might have been with covered it up instead of going to the authorities...?
What do you think?