You can actually just walk in and get stuck, I just did.
Valarie says to go battle Neved and get the key, so I went to the throne room where he was supposed to be, and got stuck. I reset to an older save, went back, talked to everyone on he bottom floor, inspected as many things as I could, saved, went back to the throne room and got stuck. Then I loaded up the save and went outside the castle, which caused the guards to appear again as if nothing happened, so I walked in and out of Neved's room, the guards were out cold again, I went through the same process as last time, and... got stuck for the third time.
I have no clue what I'm missing here but so far it seems to be easier to get stuck than to trigger the fight. Do you have any tips?