I've had a little time to consider voluntary missing but the thing that gives me pause about that, is that by all accounts she was living independently, not under the thumb of somebody like controlling parents or anything like that. Why would she feel the need to disappear? I suppose the school angle is valid but it's not like she would be checked on every day.
So really, I am very worried that this is either a case of self harm or foul play of some sort.
I've read everything in the thread, but forgive me for asking if it's been posted, have we heard anything about her cell phone? Is it missing too? When was the last time it was used and where did it ping?