From what I have been able to glean, Polina Agureyeva is the singer. The song is “My Little One” from the Russian film “A Long Goodbye” by Sergei Ursuliak.
This song is beautiful and so moving. It’s not classical guitar, but that doesn’t take away one iota from the moment. I’ve been humming this song for a couple of days now!
This song has hooked me. I want to see this film.