You don't actually need to kill her if you talk your way out of it or intimidate her.
The rune has nothing to do with getting out of that room though but there are clues that tell you about it. Just read everything you find.
I was lucky enough to have one of my NPCs not make it into the room when the door locked. There's a clue written on a note in that room outside - nuff said.
Yes, happened to me once with my party stuck in the door and 2 out but I think that's not supposed to happen because she holds you hostage unless you poision yourself or you talk her out of it. If you try to escape she attacks you.