Syl is feared by her subjects. Most worry that her paranoia may lead her to act rashly and kill or torture them. Many of them want her dead because of her ongoing relationship with Thadon.
After restarting Xedilian, Lord Sheogorath will ask that the Hero learn more about both Thadon's court of Mania and Syl's court of Dementia. She will ask the Hero look into the current threat on her life. She will assign Herdir to help and allow them to proceed as they see fit.
After relighting The Cold Flame of Agnon, Sheogorath will ask his champion to replace either the Duke of Mania or the Duchess of Dementia. If the Champion decides to replace Syl, they will need to follow tradition and assassinate Syl and take her heart. It should be noted that once the Hero finds Syl she will attack on sight wielding her hammer Nerveshatter.
If Thadon is picked to be replaced, Syl will become outraged to see Thadon killed and will join the Forces of Order.
If Syl was not killed and replaced as Duchess, she will be found leading the Forces of Order underneath the throne room in the fountainhead. She will need to be killed to stop order from overtaking.