Worried about my sisters behavior

I don't quite know where to begin or if I am simply overreacting or if my intuition may be right. I have never written anything on here an my mind is kind of all over the place so I apologize in advance. To start it off as clear as I can, I am a daughter to a mother who has had a very rough road with pill addiction, suicide and mental health problems. My sister is what is concerning me given the experience and signs I have learned along the way of having an addict for a mother. My sister lived a majority of her life with severe anxiety because of things my mother has done and that my sister witnessed. Leaving her to stay locked in her house, never having a job, or even going to the store for groceries, dependent on her then boyfriend to do everything for her. She got on the approptiate mediciation and was able to somewhat get her life in order, go into smaller stores, she even tried out school and got her first job which lead her to move away from her boyfriend back home with my grandma and I. Shes now 27 she was doing great at first, following through with everything she put her mind to. Her behavior in the last few months has complete flipped, she started sleeping with random guys, one being my first boyfriend who actually took my virginity, another guy she had found love in who broke her heart. She began posting provocative pictures on her instagram and continues sleeping around with more guys. She has now been hanging out with girls who I used to be best friends with growing up but slowly realized they weren't real friends and very bad influences due to their life choices such as drinking excessively and even part-taking in taking xanax which was not prescribed. I noticed these behaviors when I would hang around them a few times with my sister and I immediately wanted nothing to do with the things they did and saw no purpose in exposing myself to that negative lifestyle I had to experience growing up with my mother. My sister has expressed how she thinks what they do is stupid and she tries to ignore it just because she doesn't have any other friends so she puts up with it. Until one day when I was with her and she had asked this girl for a Xanax pill to try. I immediately said aren't you on other prescription right now? Maybe you should talk to the doctor first before trying this irresponsibly. She said she would do that instead, the other day I found a picture she had posted on her snapchat flaunting how she had a bar of Xanax, I knew her doctor didn't perscribe it to her and she had gotten it from her friend. I had confronted her along with told my family because I was worried and I don't want her screwing up her life because she is going through a hard time right now, there are other ways. I tried to explain that to her and she and I ended up getting into an argument and how I am "perfect" and she should be more like me. This isn't what I was trying to do, my intentions weren't malicious but trying to protect her from the hell my mother has put us through and how bad my mom had gotten in the passed. I was just trying to protect her. Now my sister has been posting things about me on her social media, how I am severely mentally ill and embarrassing, the girl she got the Xanax from and who has been negatively influencing her is also writing things about me online and instigating my sister and I's arguments. Today she has posted a picture of her Xanax bar and said she loves it and its her "boyfriend" I am just trying to figure out if I am overreacting or if what I am feeling is valid and something to be truly worried about. I have told my dad and grandma about this behavior, and screenshot proof to them. Nobody has really taken me serious and she has manipulated her way to make everyone believe something is wrong with me rather than her. Ultimately I am confused on what to do, I don't want to lose my sister or her to lose herself and the things she is doing seems like she is on that path.