Re: sibling rivalry
IMHO sibling rivalry is more about parenting than anything....my younger brother is 9 yrs younger than me...I hated him almots on sight. He and his dad (at the time my moms boyfriend, now OUR dad) took my mother away from me...I went from being an only child, who was doted upon and spoiled and loved and the only thing my single parent mother cared about...to being HER. I was just there...my brother got all of my mothers love, and I was in trouble every time he cried, whined, sniffled, ANYTHING<>....my mother was short of temper to begin with (which I was used to) but after he came, it got worse...but what made it worse for me was seeing her ignore things he did bad, when I got slapped, or spanked for the same thing...bottom line; she treated us differently.
I believe resentment starts when siblings feel like their are being treated differently..as an adult I recognize it was not my brothers fault and we have a better relationship...but as a child...and even into my early 20s talking to him could bring on fits of rage...because he was so superior acting...because our mother had treated him better...she had given him preferential treatment (him and our younger brother) and HE KNOWS IT....he admitted to me that he took advantage of that, and even deliberately got me in trouble for things I didnt do, simply because mom believed him and not me.
Now, Im not saying all sibling rivalrys go this way...but this is my experience...now, I never wanted to stab my brother or wanted to geniunely hurt him...but I have said things like I wanted to hit him with a rock...not that I would do it, just sick humor...I think maybe your sister is using dark humor to cope...and it may not be anything YOU did, or any bad feelings she harbours for you...just bad feelings and memories because of situations...kwim?