Feeling pretty gutted

[Rhondazvous]

I'm proud of you MTL for making the brave decision to cut her out

When someone is so relentlessly nasty to you, they give you no option. You shouldn't have to suffer because they can't be reasonable.

The way I look at things, I try to give everyone the benefit of the doubt initially. I assume they are worthy of my full respect, and I treat them as such. If someone shows me that they are in fact not worthy of this, then I relegate them to my minimum package. I don't hurt them, and I am polite to them. But that is all they get, until such time as they show they are worthy again. It sounds like your sister has repeatedly demonstrated she is not worthy of anything more than minimum respect from you. She doesn't deserve any further effort on your part, and it's not fair that you have to suffer by making that effort and having it thrown in your face over and over. Even if you can't physically remove someone entirely from your life, you can achieve the state of mind where you don't care about anything they say or do anymore. That's what I meant by emotionally disconnecting from them, it's how my relationship is with most of my family now. I know that's not an easy thing to do, but I believe it is the solution in these situations. You can't change them, you can only change how you react to them.

Rob I have an extremely similar system, myself, actually!

I've tried describing it to a few family members, only to be blown-off, of course.

I developed this system after years of being told to "respect my elders"
even as some of my elders acted like spoiled children.

I assume everyone is worthy of respect; regardless of their age.

How they behave subsequently will determine if my level of respect increases, or decreases.

I will give an extra mead of respect to a stranger who is my elder,
because I am willing to acknowledge that they've lived through more than I have
and may be able to teach me a thing or two;

but that doesn't mean that my respect is vouchsafed to them, under any circumstances.

(George W. Bush is my elder, after all!)

I've met 8 year old boys who showed more maturity, nerve, intelligence, honour, and accountability,
than some 60 year old men, that I know.

As far as my sister goes: 

I actually already decided years ago, that once I'm out of here, I'll have nothing to do with her;
but as long as I was living here, I was constantly put on the defensive,
and my policy was to be as friendly and diplomatic as I could

..."turning the other cheek" as it were. 

And you see what it got me?  Zilch.

So be it.  She gets no more courtesy or sensitivity from me.

I respect her legal rights....nothing more.

vas-y femme
or you might say
vous allez fille
or you might say
You go, girl

You don't have to come up with a big speech about how you're not going to take any more shit. Think about what you can do (short of homicide, of course) rather than what you can say to show them it won't be business as usual.