There is a lot more information available Newquay - getting a visa can be very complicated, depending on circumstances.
Health problems in old age could potentially wipe out any savings as I don't think you can start paying into Medicare when you are older.
I am surprised that mother managed to become an Australian citizen if she went fairly recently without a job.
The sister must be a bit younger than your friend if she has a toddler - she probably thinks that her sister is single, has no commitments and can drop everything to rush out and help.
Australia is a great place but you do have to be prepared to rely on your own resources to a large extent. However, I would be surprised if there is not some more help available.
Good luck, hope they can sort something out.
Lack of public toilets in towns.