Girlfriend tied up in mortgage with ex boyfriend. What are her options?

So it's an Australian mortgage, hopefully that won't change things too much. They owe half on the mortgage, he's living in the house, failing to pay rent, he's demanding more money so they can finish a renovation, which will allow for a higher valuation when they sell it. But this plan has been idle for a year because she won't put more money in and he's broke. What can be done here?