I have a fix! It’s ridiculous but it works. Leave and grab a dead body from somewhere else. You can put dead bodies on your horse and bring it back. Throw the body repeatedly at her towards the altar in the church. Once she’s almost there it will update the quest.

I have a fix for this. It’s ridiculous but it works. Leave the area and get a dead body that you can carry. Put it on the back of your horse and bring it to the church. Then proceed to throw the
body at her towards the alter When she’s almost to the alter the quest should update.