Hi, I Have My 17 Year Old Niece Living With

Hi, I have my 17 year old niece living with me, I have always been concern with her mental health but its never been a concern with her parents, now I have her in my care I'm looking into steps on how to help her, I do believe she may have a mild case of autism but as I'm not a doctor or phycologist I'm not the right person to make this decision. what steps do I take to get help