It's closer to start the quest from the Gate of Secrets. Head for the quest marker and beware of the Seed of Suffering's group on your way. When you get to the spot, the Fortune Teller will be standing next to a group of Margonites. After you dispatch all of them (make sure to kill them off first before her), the fight will not be over. She will turn into a Mesmer torment creature boss similar to a Herald of Nightmares: the Demonic Fortune Teller. She will also spawn with six or so torment creatures at this point. After you kill her demonic incarnation, the quest will be completed.