Andrea Yates

Andrea Yates was a school friend of Sarah Jane Smith who was used by the Trickster to remove Sarah Jane Smith from existence and thereby create an alternate reality.

Biography
She died on 13 July 1964 at the age of thirteen while she and Sarah Jane were visiting a pier. After a brief encounter with a bizarrely dressed girl who claimed to be from the future, at Andrea's insistence the two entered an out-of-bounds area and a railing gave way, causing Andrea to fall to her death. Just before her fall, however, the Trickster - travelling through time to find a key moment in history that would allow the random destruction of Earth decades later - offered her a chance to change places with Sarah Jane. The desperate girl agreed and a new timeline was created in which Sarah Jane died.

Andrea lived her life, became an artist and eventually moved into 13 Bannerman Road across the street from Alan Jackson and his daughter, Maria. Andrea forgot about Sarah Jane and the accident, and indeed no one else remembered her, either, until Maria, who had been been protected from the Tricker's meddling thanks to a puzzle box given to her by Sarah Jane (a twin to a box the Trickster had given Andrea in 1964), remembered Sarah Jane and began to challenge her.

Andrea renewed her agreement with the Trickster, which resulted in Maria being taken out of time. This time Alan had the puzzle box. He was able to remember his daughter and retrieve her from Limbo. With meteorite K67 threatening to destroy Earth and Sarah Jane the only person able to save the world, Andrea repudiated her earlier agreement, and Sarah Jane was restored to history. She admitted that the death of Andrea was a catalyst in how she chose to live her life from then on. (SJA: Whatever Happened to Sarah Jane?)