I'll try to keep this story concise. I've had battles all my adult life with "trying to please" my mother and when I got a sister in law she quickly stepped up to not only please her to, but to be preferred by her over me. It is an unstated battle that she's only unhappy with when she is "losing".
For nearly 20 years I have been dealing with my SIL's need to look better in my parent's eyes than I do in every regard and up-play herself and children to them. It has been better and worse through the years. She has always gotten very hostile when she feels that she is "losing" in some regard.
Recently my father died relatively unexpectedly and when I wanted to discuss reducing some stress for my mom, (she and my brother had been causing her some) she became extremely hostile to me and ordered me to stop talking.
I was upset about the situation and several days later called to apologize, but she only wanted to scream at me. Clearly, she was aware that they were wrong, though not admitting it and instead deflected more anger at me ("narcissistic rage") for judging her. I did not argue, but only continued to clarify and apologize. She even resorted to telling me how things were different when my dad was alive and implied they had a special relationship that I wouldn't understand.
I have been very hurt by this. I did try to talk with my brother about this (also spoke to him before talking to my SIL blew up regarding the same issue, but he did not want to listen). He is also non-confrontational (like myself) and wanted to gloss this all over, but her hatred for me is clear and frankly, I regret not defending myself or saying my own piece regarding her offenses toward me.
To top it all of, my mom is okay with her hating me and has nearly said so. When I tried to have this discussion with her and I was very emotional and distraught, she even seemed to enjoy my pain. I believe that since my brother is preferred she will not admit any wrong-doing on my SIL's part because that would imply that he, an extension of herself, would be wrong.
I think my brother just wants us all to get along. I have no idea how to even cool my jets, let alone speak to any of them again.