Greetings from down under!
The military district relates to the place where the AANS nurse enlisted. Generally, nurses from Sydney NSW enlisted in 2MD (the NSW military district). However, there are quite a few nurses who were working interstate who enlisted from that state so it is possible for a NSW born and trained nurse to have enlisted in, say, 5MD (Western Australia) and her decoration would be counted against that total.
This division into military districts should be seen in the context that Federation of the six Australian states had only happened in 1901 and the military had been state based until that time; the states competed for honours thus the separate reporting (and they still do!)
There is a website that lists all RRC received by Australians -
http://www.womenaust...onours/rrc.html
and
http://www.womenaust...nours/arrc.html
cheers
Kirsty