Hi Gilarm, welcome here!

If I'm reading your post correctly, you are both trying to learn how to best navigate this relationship. That's wonderful. Is there an open communication between you about BPD ?
With due respect, I feel the information from her psychiatrist is not quite true. While there is no medication per say that is specifically for BPD, there are therapies that have proven successful, especially when the person is going willingly. Have you heard about DBT (dialectical behaviour therapy) or CBT (cognitive behavioral therapy? Both have proved to be helpful. My ex did some years of psychoanalysis, and he got much better.
You'll also find we have lots of resources here focused on us as partners.
Is there anything specific you do at the moment that you find is helpful?