Divorce and custody

My brother is working in the US. He has been there on H1 visa since 2007. He got married in 2016. They moved to the US a week after their wedding. My SIL has been disrespectful, passive aggressive and financially insecure since beginning. My brother made her joint holder in his account and we gave the money her family gifted during the wedding back to them to send to her which they did. She opened another account and it was deposited in that account. This was all done within six months of marriage. We empathized with her and did all we could to allay her fears so that she lived peacefully with him. She conceived a few months after marriage and within first year they were blessed with a daughter. My brother is very attached to the child. No one from her family went to the US to help her during pregnancy and post delivery period. She told my brother not to call anyone from our family and that she would manage. She could not and my brother after taking care of household, baby along with work has to call our mother to help out. She went there for 3 months. During which my SIL did not interact much with her she would come out of her room only when my brother returned from work and did not let my mom look after the baby. She even misbehaved once and threatened to kill herself and the baby. I counselled him and told him it could be because of post partum trauma. They should go to a counsellor. She refused. She never wanted to come to India or for any family to visit them in US. My brother put up with her behaviour for the baby. In September 2018 my father suffered a near fatal brain stroke and my brother had to ask her family to talk to her to come along. She hardly stayed with us. After 3 months they went back. On returning to US she started keeping the child away from my brother and would tell him that he touched the child inappropriately. In 2020 she even created a situation and the child was taken by Child protection services to find out if someone is abusing her. They could not find anything and sent the child back. My brother been in mental and emotional distress ever since. He has been under emotional pressure from her family's side as her elder sister is married to our elder cousin brother and his taking action could create strained relations between all 3 families. Something or the other kept him edgy and anxious all the time. She would keep gas lighting. Her family would always talk to her she would stop for few days and start again. They visited in 2021 December they received their green card. After which she made my brother's life hell. He even helped her get a job in his company to make things better, after which she transferred all his money to her account. He still stried to save marriage and on insistence from her family they started counselling sessions. While they were still going she secretively filed for divorce with exparte for full custody and restraining order. Which was denied and then simple divorce. Please suggest.