I'm really not seeing any indicators in this case that would support a voluntarily missing scenario.
While it's possible, I think it's unlikely that LS has run away.
LE has not reported that anything else was missing from the home, e.g., food, cash, any of LS's clothing other than what she was wearing, etc. If she had wanted to run away, she would have likely taken some provisions with her.
Also, given the media coverage her disappearance has received, someone would likely have seen her at some point and reported that sighting to LE.
LE's actions here don't line up with a voluntary missing case, either.
FBI coming on board to assist in the search efforts doesn't point toward a situation where LS is believed to have gone voluntarily missing.
There's no evidence we've heard from anyone that LS appeared to be unhappy...if LE had gotten any sort of inkling from anyone that she had expressed being unhappy with the Amish lifestyle and/or expressed a desire to leave, we'd be hearing and seeing very different things from LE right now.
LS being voluntarily missing would be the best case scenario.
Unfortunately, I'm not seeing anything that leads me to conclude best case scenario is the most likely scenario here.
JMO.