@Puzzles I can't copy your answer as I'm on a surf pad, but to assume that Esther suddenly on her way down from the Pic got a case of psychogenic amnesia/fugue, and that caused her to disappear and not remember who she was seems to me too farfetched. More likely would be a fall and having hit her head. Even if she would be in a fugue state, it's unlikely that she has managed to stay alive on her own, had it been spring, summer, or even early autumn that would have been possible, but not late November. If someone had found her on the mountainside showing any signs of cognitive impairment, why not take her to a hospital? The only reason for that would be abduction, isn't it what Dan thinks happened to her?
If she doesn't have psychogenic amnesia, how would you explain her staying away voluntarily alive, without money, and having left her past behind.