HOA lays out for water damage repairs. How do they get their money back?

Recently, a lower condo that had been vacant for some time, sold. The new owner was in his house when he discovered mold on the wall. He called the HOA who found that one entire wall was soaked. The leak was from the upper unit. The upper unit's owner was contacted and they immediately addressed the leak. They agreed to call their condo association insurance to report the damage. The new homeowner and the upper homeowner called for several bids. The cheapest bid was from the upper unit's contractor and the three ascending bids were taken by the new homeowner. That is where the trouble begins.

The upper owner is out of state so she has her father who lives here locally handle her business regarding the condo. He claimed the other contractors were more expensive because they wanted to do unnecessary work. The new homeowner and the HOA claim mold treatment is needed and so that justifies the increase in price whereas the upper owner's father just wants to replace the sheet rock, paint and texture. Next, the upper owner has decided she does not want to talk to the HOA or the new homeowner and says she had signed a Power of Attorney. When asked to provide this to the HOA, all requests are ignored. Now the new homeowner told the upper owner "thought they had" insurance and now they discover that they do not.

Meanwhile six weeks go by and the new homeowner is looking at paying rent at his old house and a mortgage on August 1st, so he asks the HOA for help. Within 2 days, the HOA steps in makes the complete repairs on the unit so the new homeowner can move in. The upper owner's father is presented with the bill and he says: "I'll see you in court" and walks away. What are we to do? Can we file a mechanics lien on the upper unit for the cost of the repairs? The new homeowner tried to reach the selling realtor, and the pre-buy inspector of the unit to no avail. I appreciate your advice.