The Berserker comes through a door at the back of a room with two platforms on an upper level.
Then you need to get into the room where the berserker first appeared.
Go forward a little and she'll burst through the wall. Wait for a moment till you see an opening to her side so you can run past her with-out dying.
Get into the next room copy what you did but watch out she comes through another wall! Get her to destroy the last and second to last piller on the left side of the room.
There's a glitched spot in there near the last pillar, can't exactly say where though.
Get her in the opening next to one of the fallen pillars and use the Hammer of Dawn twice to kill her.
P.S. if you stick in the door ways you can make fun of the Berserker because there's a invisible blocking thing.