Sister Being Emotionally Abused At Home

As the title says, my (25f) younger sister (17F) is being emotionally abused by my stepmom. I had the same experience when I lived at home, but I was dumb and decided to run away and had to go through being reported missing and just going to the police myself. Anyway, stepmom constantly belittles her, publicly airs anything she does wrong, shames her for almost anything she does or likes. Today my grandmother went to church with them and my stepmom came to her crying saying my sister was caught watch adult videos and had a hairbrush in her room (which like cmon, she has long hair so of course she has a hairbrush) loudly in front of everyone at church. This kind of thing has been happening for a while, and I never said anything because I knew it would just make her treat my sister worse once I left, but it has escalated, and I’m not sure what to do. To the point where my sister told me on the phone just now that she doesn’t wanna be here anymore and that she felt like the world would be better without her. I told her to call me and I would come get her if she felt unsafe or couldn’t do it anymore, but I’m unsure what the best course of action is since she’s 17. We are in Missouri, so if anyone has advice it is much appreciated.