I highly doubt that Sandra convinced Marie Coburg to give her the majority of the jewels, or that the grand duchess had lost her backbone. Sandra was the only one of her daughters on the German side of the war. She still loved her other daughters, but nonetheless a rift was created, and Marie Coburg felt intensely patriotic to her adopted Germany. So doesn't it make sense that she would want the majority of her jewels to go to a princely germanic house, and to the daughter who had nursed the German soldiers? Also, why should Sandra part from the jewels that her mother had left her? After being the "least interesting" of the sisters her entire life, she finally got to feel like the favorite. Ducky won favor by converting to Orthodoxy and becoming a Russian Grand Duchess, Missy was a beautiful, popular queen, and Baby Bee was the Benjamina, the only one allowed to wait for a marriage of love rather than rushed into one in her teens. Really, I don't find it hard to understand that Sandra would be reluctant to part with this physical proof of her mother's love.