-Block and do the attack were you jump behind her, then attack her twice. Remember to block immediately after this or she will hit you down.
-While fighting the first Boss after becoming the Sandwraith, use slow time to easily kill it. It will rarely get a hit on you, and your Sand Tank will regenerate during this time. Whenever it runs out, quickly start slow time again. Remember to stay behind it or its attack will knock you off the platform.