St. Dymphna is the patron saint of the mentally ill(and mental health workers, mental hospitals, those with epilepsy, and victims of sexual abuse.) Her image is that of a princess holding a devil on a chain leash. I was drawn to this mini-retablo in Albuquerque recently. I liked the image, particularly of the tiny captive devil.
Her legend dates back to medieval legend. According to various versions of the story, Dymphna was the beautiful daughter of a widowed lecherous pagan king. When she was a teenager, he made advances on her so she fled to Belgium with the help of a priest. Her father tracked her down and beheaded her. Not the most heartwarming story and not particularly compassionate towards the mentally ill.
Still, it is one more saint to whom to address prayers.