[Bugged Dungeon Script] Taretha Doesnt have a Script Trigger

[DECREPIT]

Hello, I have encountered with a script bug in the TBC dungeon Durnholde Keep, for the last boss, blocking me from earning the Outland Dungeon Master achiev. 

Normally, as seen in this video, Taretha unlocks a trigger, once Thrall reaches her. (I know the quality of the vid is bad, its a vid uploading during the time TBC was live)

And here's the encounter bug that I have faced on the server

 

 

So please, let me know whether am I missing something or that is there anything to be done so I can finish this dungeon as well. 

Thank you very much

Cheers