Themis-Athena's Garden of Books

Well, it turns out this book has a dual timeline (or at least significant flashbacks to the latter years of WWII); connecting the two timelines, inter alia, via the experience of a lady who was a young woman then and is now the mother of one of the characters in the (main) present-day plot line (as well as featuring in the present-day plot line herself).  So this would seem to fit the bill for the "mother" element of Russian Mothers' Day.

And since the modern-day storyline concerns a play based on, inter alia, said lady's experience in her younger days, there is also a certain potential for a "story within a story" / "matryoshka" structure, but I haven't gotten far enough yet to see whether that's actually going to materialize as well.

(Task: Read a book set in Russia, by a Russian author, featuring a story within a story (like a Russian “matryoshka” doll), or featuring a character who is a mother.)