I would tell the new love interest that you know and that she should end it or you will tell the MFT "authorities". She is not just potentially wrecking your ex-partner and new love's lives but lives of those she would potentially counsel. I don't think she would counsel "cheating"? She needs to be gotten out of the industry.

If you have a therapist, you could potentially tell them too, ask their advice and if they would help you deal with sanctioning this idiot non-therapeutic therapist.