Unfortunately if she is trying to bite now she will try to bite later. The ducks wont get big enough to intimidate her, especially since ACDs were bred to herd cattle by biting at their fetlocks. In general they dont have much fear built into them. My ACD is a little scared of our horses but then, they try to stomp her into the ground. So far she has not tried to bite but she does circle and sometimes tries to keep them in a group, pushes the goslings heinys to get them moving, etc. We make sure she gets a lot of exercise to keep her calmer in general and her 'back off' if getting better but still, she will not be left alone with the ducks, ever. The geese though will eventually be bigger than her so we will see how that goes.
My ACD does not have a dominate personality like some can have. The worst thing in world for her is to be ignored by her people.