This is tied to the sidequest "Tome of Great Value".
You'll find Ammon in the upper level of the Korlasz family tomb, at the start of SoD. She'll ask for some special moss, which can be found behind the barred door across the rope bridge. You won't be able to access this room until you've reached the climbable rope in the lower level. Once you climb that rope, the moss is in the broken sarcophagus. Give the moss to her.