I recommend you hire or buy Ceasar Milan's 'Dog Whisperer' and sit your mum in front of it! Also, I often parents don't like taking suggestions that come from their children. Try and get her involved in a dog club, like a local obedience school. It's a small time commitment, usually only an hour a week. There she will here your words, but coming from someone else, which might help. It's also a social thing so you might be able to sell her on it by saying that. Or you could say it's something you can both do together, so you can get her acquainted there before moving back to Sydney. I wouldn't recommend getting her a smaller dog instead as, like has already been said, a small dog requires just as much training and attention as a larger dog. Plus, she might feel even less inclined to get the dog out walking and socialising if it's small. Small dogs that aren't socialised often have a stronger tendency to act aggressively, so I certainly wouldn't recommend it. Good luck!