I finally beat her with my nec (power) – using woomera.9841’s build and tipps (thanks so much!!!) i made a few changes: in DS lifeforce stays longer 25% insted of moving faster in DS – while waiting for the doubles to walk in the white circles stay in DS and refill lifeforce when not in DS with axe 2 or staff 1.
My stats where a bit more offensive, less condi-dmg, more kritdmg – so I finally managed to kill her quickly in phase 2 while in lich-form. So i could avoid the problem with the rifts, because lich-form = stability.