Help me please

Okay so idk if its okay for me to even post this here but i need advice. Im not sure how to start. Its about rape. My little sister was raped when she was 5 years old and never told anyone until the time she was around 16. Im not sure why she never told me. The way i found out was from my dad. The way he found out was from my sisters bf's mom. So my sister never actually told me personally.

I brought it up. And she cried, ofcourse and for a few months would just want to be alone. Now this was about 4ish years ago. She says that she wants to speak up but shes afraid to. And i understand why. Its just that she was RAPED! Idk what to do😭 i want to see that he gets put away and called out for the shit he did. I want my sister to be free of this asshole who is presently still in our lives. But i dont want my sister to hate me for outing her. Its hard. And since i found out about it ive wanted to do something i just dont know what because i constantly see that rapist never serve the time i believe they should.

Im just lost and angry all the time because idk wtf to do. I know what i want to do but what should i do?? Please please please help and please understand why its taken me so long. I really just dont want to see her hurt anymore than she already has been by this person.