Status of Nikah after Khula through Court of Law

Assalamualaikum Warahmatullah
I and my family are currently residing in America. My sister’s Nikah was performed to the son of my father's cousin back in the year 2008 but the rukhsati did not take place as we had asked for a gap to let my sister complete her education.
During these years my sister's husband behavior with my sister was not good, he irritated her so much that developed hatred for him (instead of love). My sister seeked help from Judicial Court in 2012 for getting Khula‘. The court issued a few notices for him to appear and even published an ad in the newspaper but he did not show up. So finally the court finished the case and issued a decree of divorce which was also submitted in Union Council. Now after 4 years, there is a proposal from a man who wants to marry my sister. My question is whether she is considered free to marry again, since her ex-husband did not show up in the court and the court did the default judgement. Also, in the past he had refused to issue divorce to her despite of having many conversations with him and his family.