When she does that, hold her down and press her gently to the ground so she won't be able to move. Keep her head down as well. She is most likely showing dominance and is acting aggressive if she thinks you are not acting as like she would like. You need to break that kind of behavior and become dominant yourself. Sometimes all it takes is a few seconds of duck in lock-up grip, sometimes it takes more time.
Never had the need to try that. I have one drake that is dominant towards all the duck and my dogs, but follows me around and is gentle to both ducks and people. I'm not sure about the dogs, but I think he also just tries to chase them and his bites and body checks (like in hockey) are harmless.
Tell us how it goes.