I've read about this, but don't have the book at hand, and so if anyone can fill in the missing details....
There was a certain man that Marie wrote about, who was an advisor to her mother along the lines of a Sir John Conroy to Queen Victoria's mother. This man married the Fraulein, who was (I think) a governess to Marie and her siblings. This couple treated the children wonderfully in front of her mother, horribly when they were out of her sight. The man saved his "best" for Marie's brother Alfred (who would die in 1899 after a botched suicide attempt).
It was only after the children involved their father, that the pair of reprehensibles were ousted from the household (after a long, bitter fight with Marie Alexandrovna).