Hi IKNYC, welcome to the group

You're in a good place to connect with other parents who want to do the best they can for their children coping with BPD.
Just a few questions as we get to know more about your situation:
Does your D19 live at home with you, or elsewhere?
Does she perceive you as having final say about therapy? I ask because some young adults (i.e. 18 to 21-ish), even though they might technically know they're legal adults, still operate under a mindset of "I hate it but I guess I have to do what my parents say".
What are your concerns about DBT not working -- i.e., what are some things you've noticed that led you to that thought?
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There are certainly pluses and minuses to working with licensed vs non-licensed counselors/coaches. For example, my H and I see a marriage counselor who purposefully let his license expire, as he felt he could do better relational work outside the boundaries that licensing would require. To be fair, he worked licensed for decades beforehand, so we weren't just starting at ground zero with someone who'd never been licensed before. A potential downside to working with someone unlicensed (my understanding is that life coaches are not) could be that there is no recourse if you have serious ethical or other complaints.
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Looking forward to hearing back from you, whenever works best for you;
kells76