Inlaw is promoting H's affair!

[ReDesigner]

I'm so mad I could just spit! Spit at my sister-in-law for attempting to show my daughter a photo of the OW. The OW is a friend of my sister-in-law. They live in the opposite coast from where we live. My daughter, who was visiting the other coast staying with our friends, smartly refused, but to make things worse, her cousin also started telling her all about the OW and that her father slept with the OW. I was livid! Apparently my H told his brother's family not to say anything to our daughter while she was visiting. Obviously that fell on deaf ears.

This sister-in-law has never been a friend of mine, although at one time, when we were newly-weds she hung out in the same social circle. She proved to be both a user and a maneater and could hardly wait to get her claws into my husband's brother. ( I don't know what possessed her to say to me after meeting his brother that she hadn't had sex in a year and she was dying to meet a man!) Anyway, she has proven in the past that she only acquaints herself with people who can "make her look good" - either people who have prestigous jobs or a lot of money. She collects names and business cards like others collect stamps. She and the OW have been friends for at least 20 years and I actually met the OW at one of her dinner parties years ago. Now, my spouse has said he just met her on a plane, which I know is a lie.

I'm furious at this sister-in-law who assumes that this relationship with her friend is OK. She almost appears to promoting it.

Should I call her and tell her to stop meddling in my family? She has displayed zero... no negative emotional intelligence. Both she and her kid have really hurt my 14-year old daughter, yet think nothing of it. Some mutual friends have speculated that she wants my husband and her friend to hook-up because it would be great to have them in the same family. Yet, her own marriage is on shakey ground, too.

Should I bother with this meddlesome idiot or should I warn her that she is totally out of line in trying to help destroy my marriage? I realise the blame must lie with my husband mostly, but he doesn't need help!