'Little Mother of Russia' is not bad. There are other biographies and books on the subject that fill in the picture of the Dowager Empress better. Try these :
Empress Maria Fiodorovna, by A.I. Barkovets and V.M.Tenikhina, Abris Publishers, St.Petersburg, 2006
Empress Maria Feodorovna's Favourite Residences in Russia and Denmark, by Galina Korneva and Tatiana Cheboksarova, Liki Rossi, St.Petersburg, 2006
A Royal Family - The Story of Christian IX and his European descendants, by Anna Lerche and Marcus Mandal ISBN 87-15-10957-7 - chapter entitled 'Love and Revolution - Maria Feodorovna's Fate during the Greatness and Fall of the Russian Empire' - an excellent account with privileged access to private royal archives and interviews with members of various European Royal Families