What chat box says and what to do: The QBD takes a huge breath - Prepare for fire wall(s) The QBD's concentration wavers; the X artefact is now unguarded - Click on the red crystal The QBD summons one of her captive, tortured souls - Prepare for souls She turns green/blue - She's weaker to mage when green and melee/range when blue. Doesn't matter much. The QBD gathers her strength to breathe extremely hot flames - Go to the sides. Standing in the center will hurt.
I also highly recommend a Steel titan + summoning potion + charged helm. Spec restores with claws are helpful too, especially to speed up the final form.