The Problem:
I could not find [champion=593] for the quest One Last Adventure. I looked where she should be originally (Trueshot Lodge 41.6,75.0) and also to where she moved after a bunch of quests, the South Tower (43.6,26.6), and she was not in either!
The Solution:
1) She now could be one of your followers and you sent her on a mission! Go inside the class hall and check the Scouting Map. Wait until the mission is over and check the two locations I mentioned above.
2) If solution #1 did not work for you (it did not work for me either). Go to the Scouting Map, at the bottom you can "Assign a Champion to assist you in the Broken Isles". Assign her! I went outside and she was still not there (or with me, she only shows up when you leave that area). I went back to the Scouting Map and unassigned her, then I went outside where the quest mark shows and voilà, she was there! Bug? I think so! I also did not have to switch to the spec I wanted to do the quest.
Obs: In my case, I had finished all the campaign quests.