So, the actual question here is "What can I do to get her to see what a self-serving bitch her sister is?" and the only honest answer, as always, is "You can't. You cannot change other people's minds for them."

What LW ought to have done is start talking, in less polarizing terms, about the effect of SIL's little requests on their marriage. And if LW had been doing that all along then probably this blow-up would not have happened.

But LW hasn't done that, and that is why everything is screwed up. So, in conclusion, don't fucking wait seven years to tell people things!