How to help someone who is diagnosed with Autism late in her 30th?

Hi,

I am not sure if this is the right place to discuss my case. It is a long story. I have a sister who has autism. She managed to go to School until she got a master of science degree. Unfortunately, my parents were not that educated to notice that she has autism. We were many kids. My parents, my siblings and I treated her all the time not in the good way because we were ignorant about her problem. For instance, if she was slow in doing something or not doing things in a correct way, we were pissed off and treating her as if she is a normal person who messes up things. It took us many years until we found out that she has autism. She is forty without a job and living with my parents. Recently I noticed that she is being sexually abused by men. I think she is trying to find the love and care that she could not get from home. I am very sad and depressed as her sister and even hate myself for not being able to help her. I hate myself for those times that I was not treating her well. She does not know that I know what is happening to her right now. She leaves home most of the time in morning and comes back home at night as I heard from my mom. After what is happening to her now (being sexually abused), she is even more depressed and looking like someone who is not attentive at all to the people or things around her. I am so worried if something even worse happens to her. Every day I ask myself What if she runs away home? what if she gets killed by one of these men? What if she gets some bad disease? I even dont know how can I convince her to see a therapist. 

I am not sure if anyone can give me an advice, but if you can I would appreciate it. Today I just joined this community, because I thought maybe there are some people in this community who have similar experience and can share it with me.

Thank you