Also, looking into Mathias, WV where her last known activity may have been (I have NO idea what that even means) There is nothing there. A post office, a church and a few houses! It's just south of someplace called "Lost City" and that's pretty telling.
What on earth could she have been doing there? In 1980 the population of the COUNTY that Mathias is in was only 10k people.
I just thought of something. I wonder if she went to church youth group. There is a popular youth group in town (that has a history of accepting people of any faith or even no faith) that has been sending 100s of teens to Appalachia on service trips since 1978 and rural West Virginia is usually one of the options. Maybe she met someone the previous summer and had kept in touch?