Does the name of a diagnosis matter? She is a difficult person. You’ve done your best to stay in relationship with her despite her terrible behavior. At her age, she is unlikely to change unless she somehow realizes how sad it is that she is missing out on having a positive mutually supportive sibling relationship.
I can’t make a diagnosis, but I can confirm that she is a troubled person. I can also sympathize with you about how difficult it must be to put up with her.
To answer your question about how to get along better with her: You may not be able to do any better than you are already doing. The key is not to expect anything from her. You know who she is. It’s unlikely that there will be any new information. All you can do is be reasonable yourself and not let her behavior get to you. If you are having trouble doing that, it might be helpful to see a counselor to get some practical advice.
I wish you well.