Sarah Jane Smith was an investigative journalist, but now solves crimes with the help of her friends Josh Townsend and Natalie Redfern (Nat- voiced by the Sladen-ators daughter.) She enjoys peppermint tea, used to drive a VW Beetle and has been known to go under the fake name of ‘Lyla Quest.’ Miss Smith is also single, according to Wikipedia this is because she "found it impossible to hold down a lasting relationship with any man following her experiences with the Doctor." Wikipedia have a lot to say about our SJ, and here it is...

  Sarah Jane Smith is a fictional character played by Elisabeth Sladen in the long-running British science fiction television series Doctor Who. An investigative journalist who was a companion of the Third and Fourth Doctors, she was a regular in the programme from 1973 to 1976, returning most recently in the 2006 episode School Reunion, opposite David Tennant as the Tenth Doctor.
  Sarah first appeared in the Third Doctor serial The Time Warrior, where she had managed to infiltrate a top secret research facility by posing as her aunt, Lavinia Smith, a famous virologist. She sneaked into the TARDIS while the Doctor was preparing to follow the trail of a kidnapped scientist through time, and became embroiled in the subsequent adventure.
  Sarah then found herself working with the Third Doctor and UNIT on a number of occasions. She was present when he regenerated into the Fourth Doctor at the end of Planet of the Spiders, and continued to accompany him on his journeys through time and space.
  The exact placement of Sarah's adventures with the Doctor is part of the UNIT dating controversy. In Pyramids of Mars she stated that she was "from 1980", which implies that her adventures with the Doctor took place in the near future from the time of broadcast. However, fans continue to argue if she meant 1980 as the year she came from, the year she last returned to Earth, or the year she believed it was in her personal chronology.
   from wikipedia.com