HI Youngjeudi,
Sorry to hear your young australorp is causing trouble. My boys are having problems with the roosters these days but not the hens, not even the australorps. Wish I had an answer for you. WHen a rooster rushes me and is close enough to touch me, I will use my foot to push him back. My hands are often busy and not able to carry anything else that could be used to defend your space. I have read that in the absence of a rooster, a hen will fill the job description. Maybe that's it.
Thanks for the PM.