Matrimonial issue. Nature. kindly help.

My sister got married to her boyfriend at the age of 23 alien my parents were not in favour of that but later because of her beating as they agreed initially everything was fine my brother in law and their family is very good but because of some issues my sister is not able to adjust there she came and she came back to our house leaving her in laws along with 2 years of daughter and now she is refusing to go back. there is no major reason of any issue between my brother in law and her, just little little day to day household and habitual issues of both. Problem is now she is from last 1 or even more years she is staying with us and not ready to go back at her in laws. Day by day she is getting more Furious more aggressive and more insecure about her daughter she don't let her talk to people wont let her go out. Even she doesn't treat maids very well my parents love her very much but still don't actively suggest her anything about going back coz of her aggressive nature. Kindly help.