So is Tasha Lem a previous regeneration of River Song because, for one she can fly the T.A.R.D.I.S and the Daleks claim they killed her multiple times before extracting information about The Doctor from her*. She mentioned River by stating that the Papal Mainframe engineered a psychopath to kill him, but that information could easily be obtained from a database such as the T.A.R.D.I.S, just as River discovered who she was by using the Teselecta to change into River Song.
*Most of you will probably say that the Daleks killing Tasha would have triggered the regeneration cycle, unless she chose to remain the same…( I believe that’s possibly)