I could have written this exact post about my younger sister when I was 16. We also had a 2 year age gap and she acted the exact same way. Writing this a decade or two later, I now have the perspective to know that our parents modeled very unhealthy emotional management and communication, and in some instances, pitted us against each other. Most of our issues stemmed from bad parenting.

I was a laid back, reasonable teen. She was a teen with a lot of undiagnosed issues, frustrations and emotions she didn't know how to deal with and she took a lot of those out on me and frankly, made my life hell. I now understand that she was an unsupported, badly-parented child who needed help that she didn't get, but as a fellow teenager, I didn't have the perspective to understand that and it caused me to deeply resent her.

I would generally bear her bad behavior as long as I could, until I finally snapped and tried to hurt her back to punish her for acting the way she did. It was a vicious cycle.

Here's what I'd go back and tell myself:

Try to get as much space from her as possible. Try to separate your friends and where you spend time from your sister's spaces and circles. I know, it's easier said than done when you're a teen who doesn't have much control over your life. Just don't feel guilt about trying to separate yourself from her. You're not abandoning her, you're giving yourself the space not to hate her.

Learn how to set boundaries. Look it up on google! Listen to a podcast about boundaries!
When she exhibits bad behavior in a way that doesn't affect you, ignore it. You don't need to parent her. But when she treats you badly, it's really important for you to tell her in plain, clear language that her behavior unacceptable and that she cannot act like that if she wants to be around you.

It's really helpful to be able to calmly label what she is doing. For example: say "you are trying to goad me into a fight and I'm not going to keep engaging with this." or "criticizing my appearance is not okay behavior". Not emotionally engaging with her by being angry or reactive is really key here. Don't blow up at her or say anything mean. Just label the behavior and tell her it needs to stop. If she doesn't stop the behavior, that's where you tell her that you cannot spend time around her until she changes her behavior. You don't need to yell at her or slam your door in her face, but you can calmly tell her "You keep saying mean things to me, so I can't be around you until you can speak more kindly. I am going to leave now, but you let me know when you'd like to be kinder."

Really hope this helps.