I generally can only beat Tavion through dodging and sabering. Diagonal scissor swipes aswell as side to side ones seem to work well, forward+left+attack then back+right+attack does diagonal, just right left with attack does side to side. Jump up when lightning goes. Fpush when she is in the air to knock her back, get in some swipes then. Or, you could just open up the console and put in god . Hope this gives you a hand.