Please guide

Hi, my family is in kind of trouble and i need some good advice. Please help us. I have an elder brother who is just married this year in May. Currently my sister in law is pregnant. Recently, we have came across some strange behavior of my Sister-in-law. She seemed behaving very odd. Once she had a mess up fight with my brother, and the reason was that she don't wake early in the morning, even for an occasion in the family. My brother asked her why didn't she wake up early, so she make a big mess out of it. She went outside half naked and shouts in the streets rubbish about my family. This time my brother take her to her family and bring her back on her parents urge. Now yesterday again she make a big mess, when she was told she should take care of little electricity wastage. She again made a big mess out of it and went lying down in the gallery shouting. My family is totally terrified out of her acts now. My father and mother don't even want to live in their own house. They are terrified that she could do even worse try suicide or blame them bad for any thing. Please help us and what should we do.