This is a question for a test (not real life)
This is a classic test question that has to do with the balance of privacy of patients vs the protection of property/health/life.
To answer this question, see Tarasoff. https://en.wikipedia.org/wiki/Tarasoff_v._Regents_of_the_University_of_California .
I think that the therapist should brake the duty of confidentiality and report her patient to the authorities, because there is a credible danger to life in the future.
