Baroness Sophie (Isa) Buxhoeveden was a lady-in-waiting to the Empress. She wrote what's often considered the first researched biography (rather than a memoir) of Alix, which you can read here:
The Life and Tragedy of Alexandra FeodorovnaShe also wrote
Left Behind: Thirteen Months in Siberia During the Revolution which tells what happened in her own life after her separation from the Imperial Family. A third book by Buxhoeveden is called
Before the Storm, but I haven't read that one!
According to Greg King & Penny Wilson in
Fate of the Romanovs, Buxhoeveden allegedly betrayed the Imperial Family by revealing the location of their hidden jewels (aka: "the medicines") in exchange for her own safety.