I don't believe Cass is a sociopath. But I believe she can have a breaking point and go down that road eventually.
So far, Cass's dynamic in the game's plot is much closer to that of a "tragic character" than a chaotic evil villain.
Much of this first impression is due to her nihilistic, pessimistic and sometimes even sadistic worldview; however, if I could draw a parallel between her and another character, I would compare her to Rust Cohle, who also loves to use an apparent misanthropy to hide his past traumas. Cassandra creates an unpredictable and bloodthirsty persona to use as a coping mechanism.
I personally believe that she can be redeemed, worsened or used for a greater good. It all depends on the player's actions.