Time can sooth the problems. When we try to file a case in a family dispute we will thing a lot because when we start a litigation it may consider wrong way in other party and lead to end the relation.
In your case your sister can choose The Protection of Women from Domestic Violence Act, 2005 for her help. She can also choose 498A . IPC 498a was made to protect a woman from injury to life or limb, or mental harassment to the extent to drive her to suicide.
Major relief’s are available under Act
1. Protection Order (Section 18)
2. Residence Order(Section 19) , alternative accommodation
3. Monetary Relief(Section 20) (seek maintenance , return of streedhan
4. Custody Order(Section 21)
5. Compensation Order(Section 22)
6. Interim / Ex parte order(Section 23)
7. Breach of Protection Order (Section31) Violation of the Protection Order cognizable and non-bailable offence (Section 31-32).