Future sister in law drama. Need help.

Hey ladies I need some advice. Before I was engaged I was dating my bf for about three and a half years and just recently feb I got engaged. His younger sister is 20 years old and I’ve always gotten along w her . We would hang out and stuff and we’ve gotten a lot closer too. Fast forward she left home due to her parents don’t agree w her relationship bc her bf been in jail and it’s just a mess. She left her family back in March and so she’s been blaming me thinking I spread lies about her to my in laws and she’s assuming I’m talking behind her back when I mind my business. (Older then her btw) well itsnot my fault her bff snitch on her and it’s dramatic. The sister would call me fake and tries to threaten my relationship w my fiancé. She never came back home and my fiancé kinda doesn’t care about her anymore but it’s bothersome. Should I block her ? She’s family still but it hurts bc all I’ve done was care for her. I even tried to explain to her and even told her I love her as she was my own sis.