Who is Xenia Popova from The Case of Comrade Tulayev and what is their importance?

Xenia is the daughter of Popov and a friend of Rublev and Dora. She is a beautiful young woman with wide, well-shaped, blue eyes fringed with long lashes. Rublev cannot believe that such a horrible person as Popov is her father. Xenia is sent on a mission to Paris, France to learn about a new printing technique for cloth. While she is there, she learns of Rublev's arrest. In trying to help save him, she is arrested for treason and brought back to the U.S.S.R.