Lend money to wife's sister but not returning now and threatening us

My brothers wife's step sister had planned to take revenge, as she was unhappy in her life. She is a NRI in US. She came to India often but nvr stayed with us. After my sister in law died she came n stayed with us for 3 months. She used to cry everyday that she hs no one to take care of her. She planned to settle in Bangalore n bought a house n asked my brother to help her in renovation. She promised to pay him. After the work was over, when he asked for money she started to abuse him n hit n torture him. Now she has stuck posters saying that he is a child molester. What action can we take.