Unusual on AFF maybe, but very common in family history.
I'm assuming that your mother doesn't know the name of the hospital she was born in - or if she was born in a hospital, as o
pusman points out.
Visit (don't telephone) your local large family history society - I assume it will be the
Queensland Family History Society and put the problem to them. They should have resources, or at least 'how tos' for Germany. In particular, I would think you would want your mother's birth certificate, which should name the place and/or institution of birth. You, or your mother, may be able to obtain this on-line; some places you can, others you can't. Again, the QFHS should be able to help you. They shouldn't charge for such assistance.
Secondly, Ancestry.com host a large number of 'Rootsweb mailing lists' for areas and subjects all over the world. People subscribe to them to ask questions exactly like yours and there are always very many people, family history enthusiasts, are happy to help with advice, and even local 'look ups' if the enquirer is from overseas.
To start with, you may want to join the
Australian-German mailing list. Don't worry about 'dumb (or vague) questions' - its all a very friendly and helpful community. You could ask about how to get a birth certificate there too, if you want to go down that route.
Alternatively, here is a list
Germany mailing lists. Choose the one geographically suited to Husum. If you are unsure, choose one you think might be right and send an e-mail to the Administrator of that List (they come up when you click on each list) and just ask which list you should join.
.
Lastly, you could visit the
German consulate in Brisbane - they should be able to assist with resources in Germany, if needs be (again, maybe about a birth certificate).
Happy for you to PM me if you need particular help.