I don’t see how your therapist isn’t emotionally regulating herself or not maintaining composure. From what you described she is very much regulating herself by maintaining her boundaries. If my boundaries are not to talk on the phone after 10pm but a person kept calling, I’d not speak to them. Not because I don’t regulate myself or can’t maintain composure but because my boundaries are not talking on the phone after 10pm. It’s nothing to do with regulating my emotions. In addition it sounds as your therapist was put into a position of enforcing stricter boundaries after you threatened to kill her.

Having said that, you might need more flexible therapist who is willing to stay after and answer the phone at all times and have looser boundaries. If this therapist causes so much turmoil, please consider a different therapist if possible. Many people on here report that their therapists will talk to them after hours.