Stell (278) explained that a dish-cover is one of those dome-shaped metal covers placed over plates or platters to keep the food hot and steaming until ready to serve. Rose Maybud's dish-cover was presumably silver-plated. That would lead us to infer that her mother might have been an unmarried servant in some manor house. Who knows? Rose might even be the unwanted result of one of those daily crimes, hence a close relative of Robin's; so there is the germ of yet another Gothic plot. Perhaps you may recall that the eponymous hero of Melville's Billy Budd explains that, "I heard that I was found in a pretty silk-lined basket hanging one morning from the knocker of a good man's door in Bristol" (212). And Jack Worthing, in The Importance of Being Earnest, was found in a valise in London's Victoria Station (313).