Oh dbt-sis, I'm so sorry to hear of your pain. My heart goes out to yo and your sister. Allow me to also welcome you to BPD Family. You've come to the right place! Here you will be able to learn tools to improve your relationship with your sister and also you'll be able to talk to people who have been in similar situations.
Here is a good video about how you can reduce conflict with a person with BPD (pwBPD).
Video-Tools to Reduce Conflict with a person suffering from BPD The video uses the relationship between a couple as an example, but the tools in the video can be applied to any relationship between a non and a pwBPD.
Is your sister currently in therapy?