Ahhhh Calluna - this sounds like a very tricky situation - hats off to you for trying to help your mum even though she sounds like she's hopeless at helping herself.

Rather than seeing a lawyer, maybe see a financial planner yourself first without your mum and see what options there are. I agree that the first priority should be buying a house then ask them what arrangements could be made to pay your mum an allowance from the money that is left with the remainder being put into a high interest account or similar where she can't easily get to it. Or straight into her super (not sure whether she's at an age where she can access it yet).

Then you can sit down with your mum, set a budget for the house/any furniture, decide what she needs to live on week to week and how much should be put into savings/super.