I just killed the Deacon and I have the doll, I have earned Sirris' respect and I can summon her for boss fights, but I can't find her summon sign on the bridge. Am I supposed to do something else?
Have you activated the bonfire after the barrier yet? As far as I know you have to activate that bonfire in order to make her sign appear on the bridge. It's on the far end of the bridge - where you came from the Catacombs.