My sister said she knew that my BIL was in contact with my wife. She told me that he loves her like a little sister. I told my sister this is BS.
People have strong reasons to live in denial, no one particularly likes change, especially when it comes to their marriage and home life. You suspected that she knew anyway, and it appears that she does and chooses to believe it's no big deal. Don't push the issue with her, it will just make her resent you.
