In Russia at this time military ranks for women were honourary and given to women of high stature. Catherine would have a military rank being the monarch at the head (symbolic) of the troups. It is in normal that princesses would be honourary commanders similar to the way Princess Ann or Princess Margaret were named "Colonel-in-Chief" of various Canadian or British regiments. Woman at that time would help tend to wounded troups but would not be part of a fighting unit. This changed under Bolshevism.

Here is a book that have some details from Catherin the great and the wars.

https://books.google.es/books?hl=es&lr=&id=5kFpAgAAQBAJ&oi=fnd&pg=PP1&dq=catalina+the+great+russia+military&ots=GJqTfytln6&sig=Rvf89MaOZiFR9I3QX5qu7wQ-lqs#v=onepage&q&f=false

In a slightly later period (early nineteenth century) there was one Nadezhda Durova, known as "kavalerist devitza" (cavalrymaiden). She joined the army and raised to the rank of captain. Her memoirs are published.