A professional who provides psychological therapy. This is a straightforward occupational title.
She works as a psychotherapist at a hospital.
心理学者 is a psychologist, often an academic researcher, while 心理療法士 specifically refers to a clinical practitioner providing therapy.
精神科医 is a psychiatrist, a medical doctor who can prescribe medication, whereas 心理療法士 is a therapist who primarily uses talk therapy and may not have a medical license.
Compound of 心理 (psychology), 療法 (therapy), and 士 (professional, practitioner).