I would like to help you both to find your mother's ship. You will find the information at National Archives of Australia in Chester Hill. Go there. They will help you find it. Not only did I get the ship name but I got my parents immigration papers, all of them, their passport photos, and the dates they left Germany and where they ended up in Australia and the dates.
My parents also came from Poland and I was born in Cowra and when that closed, were lived in Greta Camp.
To finally find this for me was really exiting and I hope you have as much fun getting it.
p.s. If one of your mum's got married in Greta Camp in a Catholic Ceremony, I have found a picture of Father Flynn also who was the parish priest.