B.R.
I'm no expert but It sounds to me that what goes on in your household should be kept in your household. It seems as if you did not have any problems with her until you started consulting with her. Are you seeking some advice from her? It seems that she has not been too helpful and has made matters worse.
I would just learn the experience that you cannot tell her anything. I would be as sweet as pie to her and sister-in-law and treat them the way I would like to be treated. And maybe this would help them to see how petty they have been. At the same time, I would only discuss my business with someone whom I could trust.