My twin sister has turned violent and turned into closet alcoholic

Dear Gaone Please keep my identity anonymous. My twin sister has been married for some time now. She has always been a teetotaller and the most reserved, gentle, sweet, rational, diplomatic, polite, even – tempered, understanding and calm one in our family whereas I am the complete opposite despite being birthed by the same mother a few seconds apart. My concern is that she has now become a closet alcoholic. She constantly erupts into violent fits of rage over minute issues towards everyone in the house more especially her husband. I am witnessing this first hand from the six months that I have been temporarily staying with them. She long told me that her husband is emotionally abusive, but it never really sank until I recently discovered that she has been a closet alcoholic for two years now and after seeing her repetitively overreact. Her husband is a nice, loving, responsible man who takes good care of his family and never hurts a fly publicly. My sister has shown me a barrage of barbaric and earth-shattering text messages and recorded conversations between her and her husband exchanging a litany of abusive words during some of their conflicts. From their recorded conversations, I am speechless that her hubby is truly emotionally abusive. I am also shocked to the core that she equally retaliates by making venomous and abusive utterances to her significant other too. I know beyond a shadow of doubt that she was never like that; she says that she has turned into a monster because of her abusive husband and I unequivocally believe her. There have also been a few times when I returned from work during my stay with them and found her face bruised from physical abuse. She’s shown me videos to verify the new development of physical abuse in their union. I am worried that my sister is not ready to exit the relationship despite being aware of all the legal remedies available to her. Kindly advise.