Looking at her through the lens of mental illness can be comforting for some people. As long as you do not use it to excuse her verbal and emotional abuse it is fine I think. Even disordered people are held accountable for their actions.
It sounds to me like you did very well with ending the conversation, setting up boundaries (no one on ones, visits to her so you can leave etc). All of that is fantastic! I am sure it was hard to do but you did it.
I agree that if you start up contact again, it would not be wise to try to talk things out or rehash the past. Chances are it will go no where and will make things worse. pwBPD have a hard time with being held accountable and with being confronted with their own behaviors. What I find works best is to focus on the immediate issues when they occur. I say it works best because for me, that way I do not feel resentment, I do not get angry with myself for tolerating abuse and my anger does not build.
I am not sure what to recommend in terms of initiating contact. Maybe a card for her birthday if it is soon? Are there family gatherings that occur?
I will recommend that when you do get in contact, to whatever degree you choose, that you are firm with your boundaries and that you do some prep work with the other tools we have here. You can find them in the Library section of the board. See what appeals to you and then we can talk about them. Definitely do a google search on self-differentiation and Bowens family systems. You will see why you have the role of mediator and are involved in triangulation with your family. I am not pointing fingers though. all of us who grew up with dysfunction have roles that we need to shed and so many of us learn dysfunctional triangulation so you are not alone in that.
Escaping Conflict and the Karpman Drama TriangleSee what you think and we can talk about it. I think you are on the right track.