Divorce in Australia by wrong info

My sister was married on 24th March 2011. Her husband was on graduate skilled visa in Australia. She changed her details (surname, address of her husband home)on Passport and it was issued in June 2011. She went to Australia in August 2011. We came to know in August 2012 that her husband has got divorce in may 2012. she got the docs from Family court Australia in which it was mentioned that the divorce is mutual. A lawyer stood on my sister behalf and has given his office address. Moreover, the counselor form mentioned that my sisters address was Unknown. Only the husband attended the counselling. My sister never hired any lawyer nor she signed anywhere. The separation date was mentioned as 31st March 2011 only 7 days after marriage. Her husband applied for two visas in this time mentioning my sister as his wife/ dependent. Please suggest me what should we proceed against this fraud. It was only 28 days after divorce to contest this divorce. But my sister never knew abt this divorce till August 2012. Thanks & Regards Navdeep