When I say, "I was hit" it doesn't say a whole lot about me except what happened to me. It doesn't say that I have a quality of "hitness" which makes people hit me. That is the stretch which you are attempting to make when you say that the participle in the middle/passive shows us something about Mary. Thanks for your analysis of the actual language (from someone who actual knows something about it), this is the best explanation I've seen to understand the meaning conveyed by the writer and speaker.