My wife has BPD. CBT never worked for her (and it never worked for me either), her therapist switched from CBT to DBT & EMDR instead and it has better results. The problem with CBT is that it tries re-frame situations using a logical explanation to people who don't know how to talk in logical terms to see things from a different perspective. The problem is that people with BPD don't express things in logical terms, so it is easy to mis-diagnose or misrepresent and cause an invalidating statement. Borderlines are great at reading between the lines and trying to understand things in an emotional way. They can easily misinterpret your re-framing to be invalidation. So instead, DBT and a question-based approach that helps them to think through the problem themselves is so much better. My CBT therapist told me to tell my wife "that being out of town for her birthday wasn't abandonment", yeah right that'd go over like hell. BPD requires deeper introspection and CBT therapy will usually cause the client to feel invalidated