Susan Foreman's first TARDIS key

Susan possessed a TARDIS key in addition to the Doctor's own.

Susan's key was able to change shape and form, much like the Doctor's TARDIS did. In Berlin in January 1933, her key was hexagonal shaped, and she was relieved it wasn't stolen when she was kidnapped by Pollitt. (AUDIO: The Alchemists)

Susan took her key with her to Coal Hill School so that she could later use it to unlock the TARDIS upon returning to 76 Totter's Lane. (PROSE: The Rag & Bone Man's Story)

At the start of their travels with Ian Chesterton and Barbara Wright, Susan still possessed a key. When the First Doctor destroyed her key, he told her that he could make another one at a later date. (TV: "The Ordeal")