You'd really be wanting to know the agent commission, the fees the government charges you for mortgage discharge, bank break fees, conveyancer/solicitor fees and probably some other fees I can't think off offhand.
A lot, anyway.
I'm up for close to 10% in total fees and charges on the sale of mine, and that figure keeps growing every time I drop the listed price of the house as most of the costs are fixed.
Check with the bank what the break fees are if she's got a loan - it varies hugely. For us it is $700 (pretty standard CBA 'delayed establishment' fee) but that's still close to 1% of the sale price. And I think they are slugging us another $350x2 for changing the loan type and security of our other loan at the same time.