1. Are both of them staying in India?
2. ask your sister to immediately go to the nearest Govt. Hospital or Dispensary to get threated about her similar injuries and take a medical prescription which staes that she has been afflicted with injuries due to beatings/blows etc.
3. Thereafter she should immediately lodge a police complaint u/s498A of IPC alleging dowry harassment enclosing the photocopy of the said medical prescription. She can also file a DV case against her husband.
4. If she hasitates to visit police station, then she can send the said complaint to the local police station by speed post and collect track report from the postal website.
5. If police refuse to register FIR against her husband, she can file a writ Petition before the High court against police inaction praying for a direction upon the police to register FIR, investigate and act as per law based on your said complaint.
6. In her DV case, she can claim alternate accommodation and also maintenance for herself and her child.