Andrea Yates

Andrea Yates was a school friend of Sarah Jane Smith. She died on 13th July 1964, while she and Sarah Jane were on a school trip. Just before she fell to her death the Trickster offered her to change places with Sarah Jane. By doing this she lived and Sarah Jane died. No one remembered Sarah Jane besides Maria Jackson who had gotten an alien puzzle box by Sarah Jane earlier.

In the end Andrea changed her mind and let Sarah Jane live, thus saving the whole planet from being hit by meteorite K67. (SJA: Whatever Happened to Sarah Jane?)

Other notes
Andrea Yates has no known connection to UNIT's Mike Yates, who Sarah Jane Smith also knew.