The perfect role for MM at this point? If only Downton Abbey was still live; perhaps there's a similar show in the wings. I'd cast her as a maid. Or maybe as a shop lady who has recurring interactions with the main cast. Or possibly even a schoolteacher, but no higher on the social scale. That would be the way to defuse the royalty thing with a touch of irony and humor. It would also be the kind of role for which she's probably naturally suited, which is always a good thing for struggling actors.
You likely would not cast her because she is a poor actress - no talent, no star quality, no box office. You would also want to spare yourself from dealing with her dishonest and all around low and unpleasant character.