Dear biscuitsmom,
Love and compassion to you and your sister, husband and all involved.
I've just skipped around on this thread but read your last few posts.
Having a name for this toxic relationship gives the you opportunity to seek the right kind of insight from books, the web, and can lead to to the right support and counselors. I think you have a co-dependent relationship with your sister. And in addition your sister has some underlying illness/craziness/addiction(on top of craziness). Knowing the nature of her craziness can also help you target the kinds of support and insight you need.
Even if you get a counselor, get one that has a lot of experience with this type of toxic behaviour.
Something about your last few posts reminded me of some literature from Al Anon Family Groups that I read years ago. Something about boundaries and cleaning up the alcoholic's messes and about how one person's illness (alcoholism there) can make the whole family ill. Even though you may be dealing with some other illness/craziness besides alcohol addiction, the 12 steps for Families might help with concretely creating an appropriate boundary so her illness does not make you crazy too.
My cousin also highly recommends the book: "CoDependent No More" by Pia Melody, though I haven't read it and when I was less aware than now, I couldn't read the books she suggested.
As you deal with how crazy she makes you, you may be able to find a name for her craziness ... And if it is addiction, remember often, the addict is self-medicating to address an underlying emotional illness: like depression or anxiety but maybe something else like Borderline Personality, Narcism etc etc
Good luck creating an appropriately healthy boundary with your sister.