What do I need to do and do I need to get legal guardianship over my 21 year old daughter that is schitzophrinic, bi-polar and

multiple personality disorder. I do not have much money, am a single widowed mother and have two other children. She left the house on Monday morning while I was bring the others to school and when I returned she was gone. The police finally found her and said that she was in a hospital but she lied and told them she took her meds when she didn't. Social Security re evaluated her and 18 and deemed that she could not live on her own and that I was her guardian. The police say that this does not matter and will not let me know where she is so that I can help her. Please help