Sorry you are copping the brunt of your mother's outbursts, but maybe she feels overwhelmed, afraid and angry at your sister's problem and underneath knows it aint no good aiming where it fits, so you cop it.
You ask, "WHAT EXACTLY DID I DO?!!!!!!"
Of course the answer is NOTHING, but take care of your own sanity.
Nothing you have done caused your sister to be an alcoholic, to keep relapsing and try suicide.
You know that NOTHING you can do will fix her, stop her or cure her..unfortunately your mother can't see or understand this, and keeps trying to haul you into it.
Maybe she needs to blame someone, anyone and you are it.
It doesn't make sense, but that is normal for alcohol affected folks, both addicts and those heavily involved with them.
It is so hurtful and hard for you to be in this situation, but keep on as you have and put you and your needs and wellbeing first.
After all, if you get dragged in and become part of this circus, you may end up ill and then your mum would have 2 daughters sick because of alcohol.
Stay strong.
God bless