This quest is mandatory.
Then she'll need to get the Moonblade. That means finishing The Moonblade Mystery and The Moonblade Resurrection quests. In doing those, she will find The Concealed Final Will and pick up the company of Don and Nesto on her journey.
At the South Shore, Scarlett will have to deal with more Assassins outside and inside and free their hostages from the Windmill Tavern. (She might want to do some training with the warrior, Yngvar, and accept some optional quests.) Finally, she must fetch paddles for The Injured Fisherman's boat so she can ash him to row her to Venice. Giving the fisherman his paddles completes Reaching Venice (even though she's still in the Southern Bay.)
- The Undead Archon - He's in Venice.