Well, I didn’t get to the Mitchell (State Rail doing track maintenance) but I did find a ship through the wonderful website AIF project. http://www.aif.adfa.edu.au:8080/index.html
Working between the AIF Project and the Australian War Memorial embarkation section http://www.awm.gov.au/research/people/nominal_rolls/first_world_war_embarkation/introduction.asp
I was able to find some details about the Hospital ship Kanowna. She departed Sydney on  25th September, 1917 and had nineteen doctors and six nurses on board. Definitely room for my character Miss Summerville to depart with them.

Now here is the new problem! After several days searching I was unable to determine that voyage’s ports of call or disembarkation. I couldn’t find anything on google, no shipboard diaries on Trove, the brilliant website of the National Library of Australia http://trove.nla.gov.au/ or the previous two websites. Peter Dennis of AIF had some  suggestions regarding the NAA http://www.naa.gov.au/ and finally their ISS Department came up with the answers: a logbook of the Kanowna, a two page document detailing the 7th voyage of the Kanowna and a book entitled Sea Transport of the AIF – all available to view in Sydney. Yay! So I’ll be back down there again soon!