Mary never was the only one. Alexandra was there before her and the only one for a long time. Mary was compared with Alexandra from the beginning and Marie will be compared with Alexandra and Mary. That's just how things are.I think they look almost the same. I don´t think that Marie have a problem with that. I rather think Mary will have a problem. She was for a long time the only one and know there is somebody who in a good position by the people, is a lookalike and have great style.
IMO Marie at the moment is seen as a nice girl who makes Joachim happy and the media seems quite fond of her, but she doesn't have Mary's popularity yet nor will she ever have Mary's position. But I think with her charming personality she has the potential to be at least as popular as Alexandra and Mary are.