Yeah that's a good point. I do work with clients who are working with mental health professionals and therapists as well. There are definitely professional boundaries. SLPs focus specifically on the speaking and communication situations and would use elements of those approaches to support the client to work toward specific communication goals. Mental health professionals and therapists work more broadly in different areas of life and would support with other areas that a SLP wouldn't be qualified to e.g. like you said PTSD, anxiety, depression. But they don't often have the specific knowledge about stuttering and communication. Depends on the client, what they're looking for, what kind of support they might need. Always recommend referrals to other professionals if needed.