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"In most western countries, including the U.S., licensed/registered psychologists hold a doctorate in their field, while licensed psychiatrists hold a medical degree with a specialty in psychiatry. Psychiatrists are physicians who have earned an MBBS/M.D. or a D.O. professional degree, whereas psychologists have earned a doctoral degree Ph.D., Psy.D., or Ed.D. " http://en.wikipedia.org/wiki/Psychologist
So a psychologist is not a physician. You need to go to a physician, such as a psychiatrist (but any physician would do), to get a letter reciting that the person is "unable properly to care for her person and property". You don't need a official form of some sort - a simple letter will do.