Problem with Mother in law

Hi to all respected Lawyers. This problem is for my sister with her Mother in law. My sister got married in 2009. Once the match fixed father-in-law met with an accident and hospitalized. Even in that sage my bother in law want to get marry. We have done with it. After marriage later 6 months Fater-in-law was passed away. First few days it went well and good. Later on motnher-in-law started harassing my sister. After every six month there will be a big clash between my sistem and mother-in-law. Elders were involved and settled the mater. Even few months My sister and her husband stayed separately. Again as per the mother-in-law request they are leaving at one place. Now again the harassment as started ( Here what I mean about harassment is she says that because of you my husband was dead, She will not tolerate if my syster do anything always shoots you are like this and no happy with the on). At one moment my sister attempted suicide at that time also elders involved and compromised the satiation. Now what is the solution, can we file complaint against my mother-in-law. Coming to my bother-in-law, he will always ask my sister to not respond to her mother and warns her mother to not to fight with his wife. still here is fight in absence of my bother-in-law. What is the best solution in this case?