Hunter tether prevents her from teleporting. You can kill her in the area before the final battle and have a chance for the strike specific loot. Then go kill her again in the main room.

https://www.reddit.com/r/DestinyTheGame/comments/3ob0iu/something_to_make_farming_grasp_of_malok_a_little/

I'm not surprised that you can kill her, but I am surprised that a loot drop is actually possible at that stage.