Yeah, that's the blame game crap a lot of them like to play. So you're supposed to feel guilty, huh?
How about you say this: I'm not the one who decided to shun you.
Or similar words that fit your situation.
Then, if she says:You know we have no choice. It's what the WT teaches us!
You could then say: So the WT really is calling the shots and you have no say in this? Maybe I should blame them for your guilt trip because they're controlling you just like a cult would.
Either she's shunning you because she thinks it's right--which is her doing--or she's just blindly obeying the WT--which is the Society's doing, because they're controlling her. Either way, this frames it so it's on her or the Society and exposes the Society's true nature. You could make her pick one or the other until she lays off. That's the same sort of mind game they are playing with you.
Another possibility, if you say: I'm not the one who decided to shun you.
She might say: You decided to leave. That forced our hand. It's your fault, not ours.
Then you can say almost the same thing: So you have no choice? Why? Isn't it your decision to make? Or is the Society making your decisions for you? I thought that's what cults do.
You'll probably get a look or some other kind of grief for that. But again, you can make her pick one: So which is it? Who's responsible for the decision that I must be shunned simply because I don't agree with your beliefs? Who do I blame?
Either she'll have to answer or lay off your case to avoid exploring this really obvious question and risk exposing the flaw in her thinking. Not to mention exposing the guilt mongering for what it is.
IsaacJ