I remember something similar happening around 14 years ago with a woman who had an upcoming wedding. She actually made it look like she'd been abducted. She had no idea that her disappearance would hit the national news and become a big thing. After about a week she wound up calling someone to come and get her. She was very embarrassed. In that case, though, she'd cut and colored her hair and went full-on "Gone Girl". I think that after all this time, if Savannah had done this then there would be word of it by now, especially after the interviews with her friends and mother. Also, there's no bus or train in Lancaster or Crab Orchard. Someone would've had to pick her up so not only would be looking at one person too embarrassed to come forward (Savannah), we'd be looking at two.
Still...not completely discounting it. People shock the hell out of me on a regular basis. I hope this is what happened.