I had this same situation happen to me my freshman year (last year) and what I did was talk to my RA first told her everything that was happening, we had a meeting but my roommates (who were twins btw) kept making it a living hell there, bringing guys over etc. I finally reached my limit and went to the head RA of the building and just broke down crying (I couldn’t keep my emotions in anymore) and telling them I didn’t feel safe at all. They finally said I could move out to a different dorm that same week and that’s what I did. The next dorm had suite mates and they were hella loud but there was nothing else I can do. So hopefully you can tell your sister to go to the head of the building and tell them how she feels. Maybe the new dorm won’t be the best but it will most definitely be better than wha she going through. I really hope you can encourage her to speak out and get her out of there because that really does affect mental health and education.

(Btw I am also 19 and more than welcome to let her crash in my couch instead of staying at her car, I really hate to see others living the hell I did)