you all mean "Maria Vladimirovna" ? that not her granddaughter, but her great-granddaughter.
Her grandchildren were:
By Kyril - Maria, Kyra and Vladimir of Russia
by Boris- (illegitimate and was not recognized) Boris Lacroix
By Andrei (maybe) - (illegitimate) Vladimir Romanovsky-Krasinsky
By Helen - Olga, Elisabeth and Marina of Greece & Denmark
Kyril's daughter was Maria Kyrilovna. so she was the only granddaughter named Maria.