Isabella

Isabella is a ship's captain and Duelist found at The Pearl brothel in Denerim. She is a formidable fighter who refined a style of fighting that others call a duelist specialty.

When you talk to Isabella she gives you hints as to her interest, and should the Warden desire, he can try to bed her as one of the ways to learn the Duelist specialty from her. If Leliana is with the party at the time of this attempt and the Warden has a relationship with her she will object and prevent the Warden from pursuing this, with a large penalty to her approval rating.