Interesting find! Recently I've seen a group photo of the Mecklenburg family (dated the 1905-1606 years) and found Duchess Marie in it! Not so great a find but this points that Marie was not a complete outcast in the family. Also in the photo her husband Paul Friedrich, her children Maria Antonia and Heinrich Borwin (very handsome young man).
Here's the photo of 1905-1906 years:
First row: from left to right - probably sisters of Duchess Marie - Alexandrine and Olga (Olga had married Count Mocenigo), GDss Maria Pavlovna-elder, GDss Alexandra of Mecklenbourg-Schwerin,
Duchess MarieSecond row (standing):
, Heriditary Prince Adolf Friedrich of Mecklenbourg-Streltz,, GD Vladimir Alexandrovitch,
Duchess Maria Antonia (daughter of Duchess Marie), GD Friedrich Franz IV of Mecklenbourg-Schwerin, Princess Charlotte Reuss (nee Duchess of Mecklenbourg-Schwerin), Princess Alexandrine of Denmark (sister of GD Friedrich Franz IV),
Duke Paul Friedrich (spouse of Duchess Marie), Duke Heinrich Borwin (only surviving son of Duchess Marie).