Only after this quest has been completed Severia will appear.
The Nerevarine has met Severia Gratius, a guard at Fort Frostmoth. Gratius has been ordered to solve the mystery of a recent rash of moon sugar poisonings here on Solstheim. Several people, including a Cult priest at Frostmoth, have been mysteriously afflicted with temporary moon sugar euphoria, and the Imperials suspect foul play. Gratius is in charge of the investigation.
After discovering who it is, she will send the Nerevarine to kill Uncle Sweetshare, who will confess to his crimes. All that is needed is his White Colovian Fur Helm, which can be handed over if asked or looted if he is killed.