My feeing is Marion did plan to disappear. Her sister and a ex husband thought it was quite possible. Oh course then the why?
Going of what we have heard on the podcast it seems very likely to do with the school. The headmaster was a intimidating bully amongst other questionable accusations. It seems she initially did get along with him but my theory is she saw, heard or found out something incriminating, she likely challenged him/them and then was accused herself. I think she was threatened and frightened. Others at the time said her normal personality changed. She was a dedicated teacher who resigned abruptly, sold her house within weeks at a large loss and gave away some of her antiques to her daughter. There was a man she didn’t tell her family about, again maybe some form of threat. Of course the biggest clue of all is the name change, such a strange name I wonder if she meant to leave some clue if something bad did happen to her? The other weird thing I’ve been thinking about is her being obsessed with getting the “scales” back to the school. *If* she had been threatened I’m thinking that was a sign to the school that she had done what they asked. Well, I know the theory is “out there” but anything is possible with this missing lady. I feel for her daughter and hope she gets some answers.