Sister took advantage of dying Mother

My mother is dying, she went in the hospital 3 weeks ago and a few days later my sister (only sibling) got my mother to give her "home" away to my niece and her "land" to my sister. She also had everything else changed where she was in charge of it. I feel like my sister has stolen from my mother because she knew she was dying. My mother thought she was coming home,she told me she was getting well and would be going home in two days,that never happened. I have tried to find where my sister placed my mother but all she'll tell me is my mother is in a Hospice. I need help! I want to be able to talk to my mother before she dies (not about her estate, she's too ill for that) but I am her only son and I want to be able to say good bye to my Mom. I need to know what if any legal rights do I have to see what all my sister has gotten my mother to sign. Our father passed away last Nov. and I have no one to turn too. Please help.