You mean freeing the prisoner?
She was dead...
Yep! You’re right. Sazza was dead in her cage in my playthrough as while I’d initially saved her and left her locked up, she must have been killed when the druids and tieflings turned on each other.
I’d not opened her cage before but I’ve just gone back and tried. I had SH pick the lock, and then as soon as my paladin interacted with the unlocked door I got an oath broken message. This makes no sense. It wouldn’t seem to be against either oath to simply open the door, eg to check whether she had anything on her that might help locate the goblin camp.
EDIT: I think it is worth posting feedback suggesting that opening the door after Sazza is dead shouldn’t result in a broken oath. I can see the argument for opening it while she’s alive being breaking an oath, certainly of devotion and probably of ancients as well.