This is not an edge case. The rules of English, if properly followed by both writer and reader, render the object of Mary's desire unambiguous, and if this is the sort of thing Doug Lenat is focused on, it's no wonder he's falling behind.
That sentence is fairly unambiguous but the construct is not. "Mary remembered all the long trips in the back seat of daddy's car, she and her brother playing games and singing along to Elvis on the radio. She missed it." What did she miss, the long trips? The back seat? Daddy's car? Playing games? Singing along to the radio? Listening to Elvis? Childhood? Family? All of the above, individually? All of the above, simultaneously? The use of "in" doesn't even mean it's the object of desire, like "Mary caught sight of a mannequin dressed in the most beautiful wedding gown, full of lace and fine detail. She wanted it." and I think 99.9% would assume it meant the gown, not the mannequin.