Alc,
Welcome to the forum and I am sorry that you are here. I have to agree with Dandy and Jake, no house guest.
It kind of sounds like your sister is a "dry" drunk. She is not drinking but has the manipulative type of personality still. I want you to read the statement that you posted. You really can't have her back in your life full time. She is mean, depressed (can't take meds to help), not sure if she is still drinking, and all the other issues that could arise. The question is, is why she is not moving in with her son. Obviously she might have burned bridges with him also while she was drinking.
Like with any alcoholic they need to hit bottom. Not drinking and working a program are 2 different things. Alcoholics need to make amends with all the stuff they have done in the past. It sure sounds like she hasn't done that and is no where near to do that with you. (most A's don't even realize the drunken stuff that they have done to us, as we remember everything)
You have a gut feeling, and i think that you need to go with your gut, believe in yourself that this is the right decision for you and your health. Just tell her no that you can't possible do it right now, maybe in the future it would be a possibility. I wouldn't give her any reason, as you owe her nothing.
Hugs my friend!!