I did that quest today, running unofficial patch 5.7. For me, the key appeared in front of the entrance to her layer (where you spawn rather). When you pick the key up, the portal should appear.
“The world breaks every one and afterward many are strong at the broken places. But those that will not break it kills. It kills the very good and the very gentle and the very brave impartially.”
THANKS! I guess I'm just an idiot, because when I replayed the battle, the key was right where you said it was and the portal opened as soon as I picked it up.
I had been looking for the key where the "body" fell and when I didn't find it there, I had assumed the game failed to drop it. Generating my own key from the console got me a key, but didn't trigger the portal.... I should have looked harder!