Sorry if I will add here some non relevant information, but at any case I dare. I thought about this family name Mouchanow and search a little. I found that family name Mouchanov (МУШАНОВ) exist, but is quite incommun. I found also that there was indeed a well known family, russian nobility of tatar root, the Moukhanov (МУХАНОВЫ). Among the differents parts of this big family and all the helpful people she gave Russia, there was a Maria Sergeevna Moukhanova: she lived in the 19th century and was the lady in waiting of Empres Maria Feodorovna, wife of Paul I. In a book about her own father, she let interesting stories about her Empress.
Then, closer to our subject, there was a Maria Dmitrievna Moukhanova, born in 1879 in Tsarskoe Selo. She also had the tittle of lady in waiting. In 1903 she married the coung F. M. Nirod. Nirod was adjudant of Nicolas II from 1905. At war time, notice this, Maria Dmitrievna worked as an assistant surgeon nurse at the Tsarskoe Selo hospital. She survived the revolution and died in Kiev in 1965.
Well, at any case I am asking myself some questions. First, did the author of "My Empress" know about Maria Sergeevna's book and used her family name in relation to this? That 's an hypothesis. Second question: who was this Maria Dmitrievna? Had she close connexion to Alexandra (I supposed not)? Would have she used her relations at court (maids...) to write this work with another surname? Or did someone used this family name knowing there were Mukhranovy at court?
Only modest suppositions, I agree.