Sister fraudulently withdrawing money from mothers account

Sir, My mother is alive and mentally incompetent. we, 3 sisters take care of her. I am the younger one and went to my in-laws house after getting married last year. My mother have Rs. 10,00,000/- fixed deposit on her name for her needs and health issues. In addition to that fixed deposit, we kept Rs. 1,00,000/- in her savings account for her requirments and emergency needs.We appoint our second sister as care taker to my mother and are offering Rs. 5000/- to her as salary and Rs. 2,500/- for my mother medicines. As she is divorced and seperated from her husband, She fraudlently planned to swallow the entire amount of our mother and started withdrawing more money than her salary. She drew around Rs. 80,000/- in this way. Hence we bloced our mothers ATM card by giving detailed objection to the bank manager. Now we request you to guide us the way to stop my sisters fraud.