She married the famous doctor Ildefonso Gallego Asorey. She worked as a teacher in Vigo for four decades. She was the first English teacher in the postwar period as she got the first position in the competitive examination in 1955. From 1958 onwards, she worked as a teacher with tenure until 1959 that she became a Professor. According to the journalist Gerardo González Martin, she got the first position in Spain when she was working at 'Santa Irene' Secondary School(Vigo). She was also a temporary Professor at the Business School for three years. In 1962, she became headmistress of the Feminine Secondary School until 1st July 1968. A bit later, she became assistant headmaster and headmistress again when Professor Piñeiro Permuy left the School. She travelled a lot to attend courses, especially during the 50's and 60's. She took part in many activities, at Texas University as well as Switzerland, Austria and Italy, among other centres.
Teresa Díaz, who was famous for being a great teacher, did not published any text book, although she wrote a monograph about the way to study English, which was published by the Ministry of Education. She was said to have had a decisive influence to get the second Secondary School for Vigo, the Feminine, where she filled the office of headmistress on two different periods. Enrique Montenegro López, who was a highly-placed official in the Ministry of Education also played an important role in this school.
She had a son, Alfonso Gallego Díaz, who was a famous otorhinolaryngologist.