When the Trickster offered Andrea Yates the chance to live, she accepted and swapped places with Sarah Jane Smith. The timelines diverged on 13 July 1964, when Sarah replaced Andrea, fell off a pier and drowned. In the altered timeline, Andrea lived at 13 Bannerman Road, Ealing and had a successful career as a painter. Luke Smith did not exist in this reality, though Maria Jackson and her father Alan still lived at 36 Bannerman Road.
It was destroyed and negated when Andrea took back her acceptance of the Trickster's offer of Sarah Jane's death instead of her's. The universe was rewritten and Andrea was killed. The only people who could remember the timeline were Sarah Jane, Maria, Clyde, Alan and the Trickster. (TV: Whatever Happened to Sarah Jane?)