I don’t know...it seems to me that anything about therapy is fine to say in therapy, from the therapy itself to the effing relationship to negative comments about the therapist’s job performance to the client’s own stuff/feelings about their stuff, however angrily expressed.

And in some ways here the client was criticizing the therapist’s job performance...but they did it by attacking the therapist’s family. The therapist certainly should have anticipated an emotional reaction, whether hurt or anger, but, seriously, should they have anticipated a statement like this, aimed at a baby born at 25 weeks who may be struggling to live and faces significant psychological and physical challenges in life due to such an early birth? I don’t think that could be anticipated. And the client is autonomous and did have a choice about what to say. “I think that’s really unfair to your clients and it makes me angry” gets the same message across without dragging innocent bystanders in.