Once you kill Ronan the Zombie in the room before the Pretox Queen, make sure you have a few health vials and at least one point into the attack where you attack an enemy in a flurry of stabs. If you have low health, do not use any of your health vials but just regenerate your health. Once your health is full, go to the circle platform where Athoxxia (the Pretox Queen) is located. Once she is done talking, pay attention to the mini-map. The red Boss icon on the mini-map shows where she will climb up on the platform. Whenever she climbs up, use Flurry on her to drain her health quickly. If she sends some Pretox spiders at you, use a power swing to dispatch them fast. If you are low on health, use your health vials. If you have no health vials, run to the bridge-like path and regenerate as you block (R + Circle). If you have a ranged weapon (bow, knives, etc.), get on that narrow bridge-like path and damage her with it. Once she is dead, teleport back to Aven and talk to the Overseer. Note: Firee based weapons are the best to use on Athoxxia.