Marie Feodorovna was Chief of two regiments, I believe:
the Chevaliers-Gardes and her Own Guards’ Cuirassiers.
In some thread ( I haven't a clue which one), the uniforms were descriibed as:
Quote:
"feminine version of uniforms of the Chevaliers-Gardes and her Own Guards’ Cuirassiers (white form fitting tunic and long skirt)"
Unquote
The Guards Cuirassiers uniform might be the one in the photographs. (The description seems accurate.)
BobG