The watchmen nearby Oriss are social, and will attack you when you attack her. Clear these before pulling Oriss.
Actually I stood on the western side of the building facing East and hit Oriss with a spell and immediately ran towards the narrow part of the river. As it turned out, no one followed except her. If they had, since the others had no damage, they would have turned back sooner than her and I could have killed her in safety across the river.
If you have good faction with Dalnir's Wheel, the watchmen will not attack when you kill her where she stands.