Of course you can post here! That is what the forum is for. You are not alone!
I remember living with my X who is an alcoholic and he would go through horrible, depressed cycles. It was awful to see, and even more awful to deal with. You have my thoughts and prayers.
Stay in touch with her. Let her know she matters, that she is loved. It's ok to love from afar and keep boundaries in place for you while doing this. Pray for her. Visit her if possible, or send her a care package.
I cannot even imagine my sibling going through this. I am so sorry for you both.
Many hugs, and many prayers!