Your home sounds very stressful and almost like anything can ignite a fight with your Mom and sister at any moment. That is difficult because you feel you have no control over the situation. That probably is true to an extent, you can and should sit down with Mom and let her know how hard this is for you to hear the fighting and violence in the home. It is important that your Mom do her best to be calm instead of fight fire with fire. If she is calm she would be able to not allow the situation to get so out of control
You can tell your Mom she needs to instead rise to your sisters level but to either leave her fighting with her self or not engage. Your sister can't fight by herself, therefore, she would just give up. If your Mom is not willing to try to work on the fighting, then, you need to take care of yourself and try very hard to get away from the home so you do not have to be exposed to this fighting.
If you can at least get away and dive into an activity that can uplift your thoughts and feelings that would be better. Listen to music, do a run or walk, go to a friends house, go to the mall whatever it takes. You are stuck in a bad spot because the adults are not acting like they should and you are stuck hearing this violence.
Your sister needs a healthy intervention possibly with professional counselor to get her what she needs. Maybe your Dad is more reasonable or another relative can intervene the situation. It isn't your place because you probably won't be able to make the changes they need to make for themselves. You sound like a very mature young woman that just wants peace in your home.
You deserve nothing less. Here is a hotline for Alcohol Counseling if you want to give to a parent or even if you want to call to see if they can advise how to make this stop and get your sister help. (800) 729-6686 National Drug and Alcohol Hotline.
We are here for you if you want to call us at 1-800-448-3000.