I need help

Sorry if this post is long in advance. I am a 23 year old going to college and supporting myself. I have a little sister who just turned 5 in November although we are only half sisters. Same mom different dad. My mom is a heavy drug user(meth) and I worry for my sisters health and safety everyday. A year ago MY dad was able to get custody of her because my mom got caught using and CPS got involved. My mom wanted my little sister back bad enough to get sober for long enough for the state to give her back, unfortunately. Not long after getting my sister back was my mom using again. I live in Washington state so usually the mother gets the child back. 5 years ago when my mom was just starting to get into drugs my little sister who is my biological sister had gotten raped due to the environment my mom brought her into and it breaks my heart. I do not want my little 5 year old sister to have anything life changing to happen to her and it worries me sick everyday to think about what could happen to her. I’ve called CPS on my mom multiple times before and they never did anything. I need help with what to do. I can’t let anything happen to my baby sister. It would break me to pieces😭