My 11 yr old sees a psychotherapist. recently she told me that if something happens to us, she wants to live with him. is this unhealthy?

Clarify.: I wonder if this is the way your son heard a comment versus what was actually said. With your son's permission, you might ask the psychotherapist. That would be a questionable boundary if it was the actual comment. How a comment was meant and how it was perceived can be quite different. Clarify. Take care.

Run the other way!: This is way, way inappropriate. Please consult a psychiatrist or psychologist you can trust and get a referral elsewhere.