Help with Nsister?

It's gotten to a point where I just can't take it anymore. After a few months of reading this subreddit I am constantly shocked by how much of it my sister (and grandmother) relate to it. I'm hoping some of you on here might be able to help me.

My entire life my sister has been "mean" to me (there are even a few photos of her choking/injuring me as a baby). As we've gotten older, while the physical abuse has tapered off the phycological abuse has become far worse. My Eparents generally say "oh she should apologise to you" and then nothing happens, or, "that's just how siblings act".

I'm not entirely sure how to describe it but I honestly don't think she can physically bring herself to do something nice for someone else without having an ulterior motive. It's like about a third of the time she fakes nice (using a baby voice, calling our parents "mummy" and "daddy") and the rest of the time you can't talk to her without her becoming enraged or scoffing at everything you say. For example she was around 13 I noticed that majority of the things she said were things she had read online, and when I tired to challenge her views she would get flustered and just roll her eyes or start calling me an idiot. She still does this now but I just try not to engage her in any sort of conversation.

She seems to find no faults with herself, and if you dare to say anything that even slightly contradicts her she'll act like you're crazy and tell you to "calm down", or as mentioned before, will just start screaming and abusing you. Then, when I would finally get fed up with the way that she was treating me, or even when I would start crying, she would immediately start telling me and the rest of my family that I was just "sulking". Even now at 18 when I go to my room to escape her I'm just "sulking" and "need to grow up".

I think she just feels like she needs to drag everyone down around her, so they're just as miserable - and let me tell you it's worked. For about half of my life I've been on the fence to wether I should kill myself and escape the nightmare that she turned my home life into, or to just wait it out until I finish University so I can move out and never speak to my family again. I think the only thing that has really kept me going was when my mum took both of us to a therapist and they told her that I was fine (albeit anxious) and that the problem sat with my sister. We never went back.

I'm sure I've missed lots of little things about her that would better convey how much I just can't stand being near her, but I would really like some tips on how to keep coping with her.

Thanks guys xx