Good evening.

This afternoon 2 friends and I were able (at great pains, might I add) to complete this dungeon.

There is a very frustrating glitch that occurs when Drodda uses here AoE attack, making her turn invisible to some, if not all, group members.
The only way to solve this is to let the only people who can see her at the time kill her (not always possible) or to reload the area by leaving/coming back (which isn't always easy/possible). Without the battle ending, this glitch will persist until everyone is dead/leaves.

Hope this is something that can be looked into for future dungeon delvers.