I don't know about MM being as alcoholic as some seem to be saying. Even less so about having an eating disorder. As someone here liked to say, much of our peculation is simply "white noise". I have to admit, much of what I've speculated falls into that category as well.
I don't know if we can ever find an answer as to what happened to her.
Occam's razor leads me to think she either perished from the elements (intentionally or unintentionally) and somehow remarkably has not been found; or she was taken (either willingly or unwillingly) shortly after her crash and again remarkably not been found.
I do agree with you on what may have happened to her. I think she could have succumbed to the elements, accepted a lift (unknowingly from a bad guy) or she was hit by a vehicle. I don't think she was abducted off the street. I have a feel she accepted a ride from the wrong person. I do think she had a eating disorder, because it explains her actions prior to the NH accident. It may be white noise, but it fills in the blanks for me. As far as what happened to her after her NH accident is anybody's guess, but the 3 possibilities I listed are my theories on what happened. I do not think she was meeting anyone and I have a feeling she didn't tell anyone she was heading north. She didn't even tell her boyfriend (phone call) when she was making the plans. In fact, she wasn't in the mood to talk.