In Forest of the Dead, just before River dies, she tells Ten that just before she left for the Library, her Doctor turned up on her doorstep, with a new haircut and a new suit, and took her to the Singing Towers. He also gave her the Sonic Screwdriver, with the ability to upload her consciousness.
In The Bells of Saint John, we had the Great Intelligence using WiFi to upload people. Did the Doctor take that tech, use it to modify the screwdriver so it could upload River, and then take her to the Singing Towers sometime between The Bells of Saint John and the Rings of Akhaten?
I notice that there are no appearances for River Song on IMDB for the rest of this season. Has Eleven met River for the final time?