Divorce

My brother got married by Feb 2015. We didn't demand any dowry from the girl side. All the expenses of marriage are carried over by us. My brother with her wife lived for two months together. My mother was living in our native place in order to leave the newly married couples happy and in privacy. She returned to my brother home after a month, My sister in law started complaining on my mother behavior. She don't want my mother to stay with them and she demanded the same with my brother. When he refused she scared my brother that she will go to mother house and file for divorce. After a week she did the same and scared us that she will file a case on divorce and dowry case. Now being four months she is not coming back also making my brother restless through phone. My brother and mother still believes that she is young and making mistakes, also she will come back. As on now its 4 months she left. Advise what we can do further for divorce. We all fed up by the girl behavior and lies she is making.