My little sis has been groomed

My little sister has a bf she’s been dating for 7 years and they started dating when she was 16 and he was 45. He’s now 52 and she’s 23, she finally broke up with him a few months ago and I was so proud of her. But I just found out that she’s back together with him. This guy has grandkids, lives at home with his mom, no career, had a whole other gf (my sis was the side piece), borrowed $ from her, only saw her on Tuesdays and Thursdays. I’m just so angry and disappointed that she got back with someone I believe is a pedophile. She’s now mad at me for telling her how dumb it makes her look at how disappointed I am cause she’s smarter than that. Should I just step back and let her live her life?