I think you're on the right track when you wonder if it's possible for your sister to be both good and misled. Witnesses tend to see the world in black and white. The longer I live, the more obvious it becomes to me that we are all morally ambiguous. No one is good or bad, we are all good and bad. It's not a pleasant realization, but I'm afraid it's true. Do your best to be more of the former and as little of the latter as possible.
I'm in a similar situation with my wife. Eventually, I'll make my feelings known to the elders and I assume I'll be disfellowshipped, which will put tremendous pressure on my mariage. I've learned to live with it. I am now putting my affairs in order so that I will have friends and a support structure in the event I am disfellowshipped. I've come to the reaization that I can't shield my wife or my mother from the consequences of their actions. If my views result in being DF'ed and that hurts them or ends my marriage, it will be the result of THEIR response to my actions, not my actions themselves. No hay de otra. Uno tiene que comportarse de acuerdo con sus convicciones.