I'm still wondering how Aleksandra would have said the girls had their periods. Would it have been something like, "Anastasia had her first monthly..." or "Olga has been ill from her monthly?"
Some examples of how this was referred to in their letters (from the book
A Lifelong Passion):
Alix to Nicky - March 3, 1916:
"Olga and Anastasia have Becker."
April 2, 1916: "Maria is in a grumpy mood and grumbles all the time and bellows at one, she and Olga have
B[ecker] [...]"
"Mme Becker" was not the only nickname, though:
January 1, 1916: "The children are lunching next door and making wonderful noises. 'Engineer-Mechanic' [period] has arrived unexpectedly and so prevents med[icine] which is a bore." (Alix is referring to her own period here)
Nicky to Alix, April 8, 1916: "My sweet Love, I want you so! Please do not have M.B. [Mme Becker] when I come home!" LOL