Hi Lever

Iam so sorry for the emotional pain you are feeling right now. My gc is still only a baby but I can imagine the pain i would be feeling too if I thought that I would be cut out of her life.
For the moment though I think you need to sit tight and wait for your dd or SIL to bring your GC over. The goodnews is that your SIL has already made the effort to do this so I think all is not lost between you and your GC. My guess is that your dd1 is feeling a lot of shame right now for her behaviour and the intrusion of privacy towards dd2 and is using deflection to take the heat off... Rationally none of it makes any sense... .but when you begin to understand the fear of ababndonment and that drives BPD behavour it begins to make sense.
... .From what I understand our pwBPDs are in such emotional distress when confronted that they are in the fight or flight mode... .and we often get to experience the either, or of the 2.
In the meantime it would be useful if you and your dh could brush up on your commincation skills, and how to use validation effectively when you next speak with dd1. Learning these skills have been a lifesaver in the r/s between me and my dd19.